To review atomic structures

Science - Atomic Structures

Dr Eeles

Key principles

The I do phase involves the explanation - indicates where a teacher would be explaining and modelling a concept.

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Moving from I do to We do involves guided practice - moving from teacher-led instruction to student-led practice.

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Check for Understanding - Formative instruction questions, posed to check whether students have understood and to inform next instructional steps.

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You do - Practice - indicates places where students will attempt questions independently.

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At the expected level for the lesson; all students should be able to do these questions.

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A small increase in difficulty from the expected level, eg larger numbers or a more complex calculation.

Extension - increased difficulty; suitable for a small number of students.

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Support - support materials, such as additional templates or questions with fewer steps.

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Engagement icons - to go in top right corner

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Whiteboard response

All students respond to the teacher’s question, showing their responses at the same time.

Non-volunteers

The teacher asks a question, gives wait time, then calls on individual students to respond.

Written response

Students respond to a prompt in a template, their exercise book or booklet.

Pair share

Students discuss with the person next to them.

Choral response

Students respond orally all together.

Thumbs up, thumbs down

Students indicate whether they agree or disagree with a statement, or whether something is an example or non-example.

Concrete materials

Teacher might choose to illustrate this teaching point using concrete materials.

Class discussion or activity

Students discuss as a class and share ideas

Calculator

Students will need a calculator to perform the task on this slide.

Spreadsheet

Students will need access to spreadsheet software to perform the task on this slide.

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In this lesson, you will need:

Exercise book or paper

Pen or Pencil

Image credit: Pixabay

Periodic Table

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In this lesson, we will:

• Review atoms, elements and compounds
• Discuss chemical formulae and balancing equations
• Review reactivity and bonding
• Review Group 1 elements, Group 7 elements and transition metals

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Starter quiz

Atoms, elements and compounds

Exit quiz

Reactivity and bonding

Chemical formulae and balancing chemical reactions

Group 1 elements, Group 7 elements and Transition metals

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Part 1 - Atoms, elements, compounds and molecules

Keywords

Atom: The smallest possible particle of a chemical element.

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Element: A chemical substance composed of only one type of atom. An element cannot be chemically changed.

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Compound: A combination of two or more different elements chemically bonded together.

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Molecule: A chemical substance composed of two or more atoms. These atoms can be the same or different.

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Atoms, elements, compounds and molecules

• All matter is made up of atoms, which contain protons, neutrons and electrons
• Each unique type of atom is called an element. There are 118 known elements catalogued in the Periodic Table - e.g. gold, silver, hydrogen.
• Compounds are made up of two or more different elements - e.g. water, sugar, carbon dioxide.
• Molecules are made up of two or more elements and can be the same or different - e.g. oxygen gas (O₂).

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Identify whether the following substances are elements or compounds:

1. MgO₂
2. Au
3. Carbon dioxide
4. Water
5. Li
6. HCl

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Y

Identify whether the following substances are elements or compounds:

• MgO₂ - compound
• Au - element
• Carbon dioxide - compound
• Water - compound
• Li - element
• HCl - compound

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Y

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Part 2 - Chemical formulae and balancing chemical reactions

Keywords

Formula/Formulae: Using symbols to show a mathematical relationship

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Conservation: A physical quantity remaining constant

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Mass: The quantity of matter an object or body has

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Subscript: A tiny number or letter sitting lower than the normal font

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Chemical formulae

• Chemical formulae are a shorthand way of representing chemical substances and the number of each atom in the substance
• A chemical formula is made up of two parts:
• Chemical symbols of the elements involved in the substance - e.g. CO₂
• Subscripts showing the ratios of elements to one another - e.g. CO₂

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Conservation of mass

• A crucial part of understanding chemical reactions, and how we represent them, is the concept of conservation of mass
• Conservation of mass states that in a chemical reactions, atoms cannot be created nor destroyed.
• This means that all atoms present at the start of the reaction (the reactants) must be present at the end of the reaction (the products).

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Balancing chemical equations

• When representing chemical equations, conservation of mass must be adhered to.
• Let’s review the example of zinc corroding in oxygen to produce zinc oxide.

Word equation: zinc + oxygen → zinc oxide

Unbalanced chemical equation: Zn + O₂ → ZnO

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Balancing chemical equations

Zn + O₂ → ZnO

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Zn = 1

O = 2

Zn = 1

O = 1

• There is currently one zinc atom on the reactant side and two oxygen atoms.
• On the product side, there is one zinc and one oxygen.
• To balance, the number of atoms on the reactant side need to equal the number of atoms on the product side.

Balancing chemical equations

2Zn + O₂ → ZnO

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Zn = 2

O = 2

Zn = 1

O = 1

• I can multiply zinc on the reactants side by two (2) to make it match with oxygen.
• Now I have two zinc atoms and two oxygen atoms on the reactant side, but only one of each on the product side

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Balancing chemical equations

2Zn + O₂ → 2ZnO

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Zn = 2

O = 2

Zn = 2

O = 2

• By multiplying ZnO (zinc oxide) by two, I now have two of each atom on both sides of the equation.
• This means the reaction is now balanced.

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Task 1

Complete Task 1 by writing balanced chemical equations for the given chemical reactions

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Task 1 - Write balanced chemical equations for the following reactions:

1. CH₄ + 2O₂ → 2H₂O + CO₂
2. 2HCl + 2Na → 2NaCl + H₂
3. C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O.

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Part 3 - To describe why elements react

Keywords

Metal: Elements typically found in Groups 1-13 of the periodic table that share similar properties.

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Nonmetal: Elements typically found in Groups 14-18 of the periodic table that share similar properties.

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Noble Gas: Elements found in Group 18 of the periodic table that share similar properties.

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Delocalised: Having no specific location.

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Monatomic: Existing as one, unbonded atom.

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Electron configuration

The shell closest to the nucleus (called Shell 1) is the lowest energy shell.

Shell 1 can hold up to 2 electrons.

Shell 2 can hold up to 8 electrons.

Shell 3 can hold up to 18 electrons.

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Octet rule and Bohr model recap

• To have a stable electron arrangement, atoms need their outer (valence) shell to contain eight electrons (even if that shell can fit more, the outer shell of an atom will only ever have a maximum of eight electrons)
• This is known as the octet rule
• The exception to this is the first shell, which can only hold two electrons and hence is stable with two

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Electron shell diagram of lithium, showing one valence electron

Electron configuration

For example, a lithium atom has an electron configuration�of 2, 1.

• To have a full valence shell, the lithium atom could:
• gain 7 electrons in Shell 2 to have 8; OR
• lose 1 electron in Shell 2, making�Shell 1 its (full) valence shell.
• It is more energetically favourable (“easier”) �to lose 1 than to gain 7.

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Electron configuration

For example, a chlorine atom has an electron configuration�of 2, 8, 7.

• To have a full valence shell, the chlorine atom could:
• gain 1 electron in Shell 3 to have 8; OR
• lose 7 electrons in Shell 3, making�Shell 2 its (full) valence shell.
• It is more energetically favourable (“easier”) �to gain 1 than to lose 7.

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How nonmetal atoms bond with nonmetal atoms

For nonmetals to stay stable with other nonmetals, groups of atoms share their electrons to mutually fill each other’s shells. This is called covalent bonding.

e.g. oxygen, a group 6 element

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How metal atoms bond with metal atoms

For metals to stay stable with other metals, groups of atoms donate their electrons, forming a delocalised field. This is called metallic bonding.

e.g. magnesium, a group 2 element

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How metal atoms bond with nonmetal atoms

For metals to stay stable with nonmetals and vice versa:

• Metals donate electrons leaving themselves positively charged
• Nonmetals receive electrons, leaving themselves negatively charged
• These negatively/positively charged atoms with more/less electrons are called ions.
• Positive and negative ions attract each other, which is called ionic bonding.

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Task 2

Fill in the table based on the information presented about bonding

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Task 2 - Answers

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Y

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Part 4 - Group 1 and 7 Elements

Keywords

Electronegativity: an atom’s ability to attract electrons to itself

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Ion: an atom that has gained or lost electrons

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Element: a pure substance consisting of one type of atom

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Compound: a substance consisting of one or more elements chemically bonded together

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Redox reaction: a reaction involving the transfer of electrons between two species

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Hydrogen

Hydrogen is chemically unique, having only one proton and one electron.

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Hydrogen

1. It can lose its one electron, emptying its valence shell and forming a positive ion, like a metal.

2. It can receive one electron, filling its valence shell and forming a negative ion, like a nonmetal.

3. Or, it can form a covalent bond with another atom (hydrogen or other) to complete its valence shell.

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Hydrogen

As hydrogen has so many different ways of bonding to other group 1 elements, its chemical properties vary.

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Alkali metals recap

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Alkali metals can be found in Group 1 of the periodic table.

They are soft metals that are able to be cut easily.

Alkali metals are highly reactive and will react readily with water and oxygen.

Alkali metals have one electron in their valence shell.

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Electron shell diagram of lithium, showing 1 valence electron

Credit: Pixabay

Halogens recap

Halogens can be found in group 7 (or 17) of the Periodic Table

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They are non metals and are highly reactive and toxic

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Halogens are all diatomic in their pure form

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Halogens are coloured, as shown in the table to the right

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Credit: Pixabay

Which halogens would go with which colour?

Halogen names: fluorine, chlorine, bromine, iodine, astatine

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Answers - Which halogens would go with which colour?

Halogen names: fluorine, chlorine, bromine, iodine, astatine

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astatine (black solid/dark purple vapour)

fluorine (pale yellow)

bromine (red brown)

chlorine (pale green)

iodine (grey solid/purple vapour)

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Reactivity of alkali metals versus halogens

• When we move down Group 1, we can see that alkali metals become more reactive.
• In contrast, as we move down Group 7, halogens become less reactive.
• This is due to electronegativity - an atom’s ability to attract electrons to itself.
• The further electrons are from the nucleus, the harder it is to attract or hold on to them.

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Reactivity of alkali metals versus halogens

• As we move down the alkali metal group, the number of electrons and electron shells increase, meaning their valence electron is further and further from the nucleus.
• This makes the valence electrons harder to hold on to, so electronegativity decreases.
• Because alkali metals want to lose their valence electron, this means that as electronegativity decreases, their reactivity increases.

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Reactivity of alkali metals versus halogens

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Li

Lithium’s valence electron is close to the nucleus, so lithium has a high electronegativity and lower reactivity

Na

Sodium’s valence electron is further from the nucleus, so sodium has a lower electronegativity and therefore a higher reactivity

Reactivity of alkali metals versus halogens

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Fluorine’s valence electron is close to the nucleus, so fluorine has a high electronegativity and higher reactivity

Chlorine’s valence electrons are further from the nucleus, so chlorine has a lower electronegativity and therefore a lower reactivity

Cl

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Complete the sentences

For alkali metals, as _________ decreases, reactivity ____________.

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For halogens, as _________ decreases, reactivity ____________.

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Complete the sentences - answers

For alkali metals, as electronegativity decreases, reactivity increases.

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For halogens, as electronegativity decreases, reactivity decreases.

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Y

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Part 5 - Ionic bonding

Keywords

Ion: an atom that has gained or lost electrons

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Chemical equation: an equation written using atomic symbols

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Ionic formula: the number of atoms of each ion in an ionic compound

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Redox reaction: a chemical reaction involving the transfer of electrons between two species (atoms/compounds)

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Ionic bonding

• Ionic bonding occurs when valence electrons are transferred from one atom to another, forming ions
• These ions are then attracted to each other because they are oppositely charged
• When metal atoms lose electrons, they become positively charged and are called cations
• When nonmetal atoms gain electrons, they become negatively charged and are called anions

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Ionic bond properties

The properties of compounds formed through ionic bonding include:

• They form crystals
• They have high melting points and high boiling points
• They are hard and brittle
• They are good insulators
• They will conduct electricity when dissolved in water or when molten

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Balancing chemical reactions between metals and non metals

Al + O₂ → Al₂O₃

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2Al + O₂ → Al₂O₃

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Al = 1

O = 2

Al = 2

O = 3

I have one aluminium on the reactant side and two on the product side. I have two oxygens on the reactant side and three on the product side.

I can add a ‘2’ in front of aluminium to balance it, but now I need to deal with oxygen

Balancing chemical reactions between metals and non metals

2Al + O₂ → Al₂O₃

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2Al + 3O₂ → 2Al₂O₃

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Al = 2

O = 2

Al = 2

O = 3

I have two oxygens on the reactant side and three on the product side. Two can’t go into three, so I need to make them six on both sides (the lowest common factor)

Adding a ‘3’ in front of O2 gives me six oxygen atoms. I can’t add a ‘2’ in front of oxygen on the product side, so I need to multiply the whole compound by two.

Balancing chemical reactions between metals and non metals

2Al + 3O₂ → 2Al₂O₃

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4Al + 3O₂ → 2Al₂O₃

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Al = 2

O = 6

Al = 4

O = 6

Now I have balanced oxygen, but I have four aluminiums on the product side and only two on the reactant side

By changing the number of reactant aluminiums to four, I have now balanced the equation

Summary of steps for writing chemical reactions that form ionic compounds

1. Determine the charge of your ions
2. Determine how many ions you will need to make your compound neutral
3. Write out the chemical equation for your reaction
4. Balance your chemical equation

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Task 3

Write balanced chemical equations for the reactions listed

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Task 3 Answers - Write balanced chemical equations for the following reactions:

• Magnesium and chlorine - 2Mg + Cl₂ → 2MgCl
• Aluminium and chlorine - 2Al + 3Cl₂ → 2AlCl₃
• Lithium and sulfur - 2Li + S → Li₂S
• Sodium and fluorine - 2Na + F₂ → 2NaF

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Part 6 - Transition metals

Keywords

Transition metals: elements belonging to Groups 3 (IIIb) - 12 (IIb)

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Valence electrons: electrons that can contribute to a chemical bond

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Periodic table of the elements

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Image credit: Pixabay

Transition metals

• Transition metals are found in Groups 3 (IIIb) through 12 (IIb) of the periodic table
• While the other metals and nonmetals only have valence electrons in their outer shells, transition metals have valence electrons in their two outer shells
• This can allow them to form ions with multiple charges

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Image credit: Pixabay

Properties of transition metals

Typically, the properties of transition metals is that they:

• have a high density
• are lustrous
• have high boiling and melting points
• can form coloured ions and compounds
• are malleable and ductile
• are good conductors of heat and electricity
• are less reactive than Group 1 and 2 metals
• can act as catalysts

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Image credit: Pixabay

Variable charges of transition metals

• Because the two outer shells can contribute valence electrons to chemical reactions, transition metals can form ions of varying charge.
• For instance, iron is commonly found as either Fe(II) (the II denotes what charge this iron has, so in this case, +2) or Fe(III) (+3).

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Image credit: Wikimedia Commons

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Task 4

Give the name and the charge for the following transition metal cations

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Task 4 - Give the name and the charge for the following transition metal cations:

• Tc - Technetium, +1
• Cd(II) - Cadmium, +2
• Fe(III) - Iron, +3
• Zn - Zinc, +1
• Sn(IV) - Tin, +4
• Ag - Silver, +1

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In this lesson, we have:

• Reviewed atoms, elements and compounds
• Discussed chemical formulae and balancing equations
• Reviewed reactivity and bonding
• Reviewed Group 1 elements, Group 7 elements and transition metals

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