Atoms, �Periodic Table �

Dr. Balasaheb P. Pagar

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S. V. K. T. College Deolali Camp, Nashik

• Matter has mass and takes up space.
• Atoms are basic building blocks of matter, and cannot be chemically subdivided by ordinary means.

What’s an atom made of?

• Even though an atom is really small, it is made of even smaller particles.
• It’s basically made of 3 tiny subatomic particles:
• Protons
• Neutrons
• Electrons

Parts of an Atom

• Proton
• in the nucleus
• + ( positive) charge
• 1 amu

Parts of an Atom

• Neutron �in the nucleus
• 0 (no) charge�1 amu

Parts of an Atom

• Electron
• in the electron cloud
• - (negative) charge�0 amu

An Atom’s Parts

• The center of an atom is called as nucleus.
• The nucleus contains 2 types of particles:
• Protons = positive (+) charge
• Neutrons = no charge, neutral
• This means the nucleus is always positive.

The Outside of the Atom

• Surrounding the nucleus is a cloud of electrons
• Electrons:
• spin quickly
• Are negatively (-) charged
• are very small.
• Have a mass of 0 AMU.

Overall Balance

• To review, an atom is made up of 3 types of particles which are:
• Protons (+)
• Neutrons (0)
• Electrons (-)
• Notice that the protons and electrons have opposite charges…what does this mean about the overall balance of an atom?
• Nucleus (+ charge) = Electron (- charge)

• REVIEW: ATOMS:
• The smallest piece of an element which still has the properties of that element is called an atom.
• Central core is called a NUCLEUS , and has a + charge.
• It is surrounded by an Electron Cloud which has a - charge.
• These 2 parts balance each other out so that the atom is electrically neutral(or has NO electric charge)

• The number of protons� in an atom is called �the atomic number.
• The elements in the �periodic table are �arranged according to increasing atomic number.
• It is the number of protons that determines the atomic number: H (element hydrogen) = 1.
• The number of protons in an element is constant (H=1, for 1 proton, 2= He helium, for 2 protons… and so on. �Argon: Ar is number 18)

• This procedure NEVER changes.
• The protons are the atomic number.
• They identify the element.
• The number of protons is equal to the number of electrons so that the element is electrically stable
• (or balanced)
• The number of protons IS the �Atomic Number

• Mass Number : the sum of �protons ADDED to the neutrons.
• Mass number can vary for the same element, if the element has different numbers of neutrons.
• When this happens, these forms of an element are called isotopes.

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• Atomic Mass is the weighted AVERAGE of the masses of ALL the natural occurring isotopes

Quick Review:

• ATOMIC MASS: The mass of an atom depends on the number of protons & neutrons it contains. It is the weighted AVERAGE.
• AMU = Atomic mass unit
• Mass number it is the sum of the � protons + neutrons.
• Neutrons = mass number - atomic number
• ( remember: Atomic Number = �NUMBER of protons, which =� NUMBER of electrons)

What about electrons & shells?

• The region around the nucleus is called the electron cloud.
• The electrons occupy certain energy levels.
• The farther an energy level from the nucleus, the more energy the electrons will have in it.
• 1st level = 2 electrons
• 2nd level= 8 electrons
• 3rd level = 18 electrons

The Periodic Table Review

You’ve got your Periods…

• Periods = rows
• From left to right
• What do elements in a row have in common?
• the same number of electron shells
• Every element in Period 1 (1st row) has 1 shell for its electrons (H & He)
• All of the elements in period 2 have two shells for their electrons.
• It continues like this all the way down the table

And You’ve got your groups

• Column = group = families
• What do elements in a group have in common?
• same number of valence electrons (electrons in the outer shell)
• Every element in group 1 (1st column) has 1 valence electron
• Every element in group 2 has 2 valence electrons.
• In fact, if you know the group’s number, you automatically know how many valence electrons it has!

Metals, Metalloids, & Nonmetals

Family #1 or 1A: Alkali Metals

• 1 valence electron

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• Very Reactive

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• Li , Na , K , Rb, Cs, Fr

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Family #2 or 2A: Alkaline Earth Metals

• 2 valence electrons

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• very reactive, but less than alkali metals

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• Be, Mg, Ca, Sr, Ba, Ra

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Family #17 or 7B: Halogens

• 7 valence electrons
• F, Cl, Br, I, At
• very reactive
• They are very reactive because have 7 valence electrons, this means they are ALMOST full and can combine with many elements.
• Nonmetals
• Halogen elements combine with metals to form compounds called salts.

Family #18 or 8A: Noble Gases

• 8 valence electrons (except He which only has 2)
• “Happy” because their outer electron shell is filled!
• NON REACTIVE (inert)�gases
• Nonmetals
• NO bonding with other elements
• He, Ne, Ar, Kr, Xe

Hydrogen: stands alone

• Gas,
• reactive,
• 1 electron in outer level.
• Hydrogen does not match properties of any single group so it is placed above Group 1.
• It can give it's electron away with ionic bonding,
• or share it's electron in covalent bonding

Family #3-12 (1B-8B): Transition Metals

• 1-2 valence electrons
• Less reactive than alkaline earth metals because they don’t give away their electrons as easily
• Bottom 2 row are the Lanthanide & Actinide series

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Family #3-12 (1B-8B): Transition Metals

• Lanthanide Series:
• shiny reactive metals
• Most found in nature

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• Actinides Series:
• radioactive and unstable
• Most are man-made & �not stable in nature