Elements, compounds and mixtures

• Atom – An atom is the smallest particle of an element which exhibits the physical and chemical characteristics of that element.

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- Postive

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- Neutral

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- Negative

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Element: A pure substance that cannot be separated

into simpler substances by physical or chemical means.

Only contains one type of atom:

lead (Pb), silver (Ag), hydrogen (H₂), oxygen (O₂).

Elements are organized by physical and chemical properties on the Periodic Table

Elements can be divided into nonmetals, metals, metalloids

Interactive periodic table

Compound: a pure substance composed of two or more different elements that are chemically combined.

carbon dioxide (CO₂),

calcium oxide (CaO),

sodium hydroxide (NaOH).

• can be broken down into a simpler type of matter (elements) by chemical means (but not by physical means),
• has properties that are different from its component elements
• always contains the same ratio of its component atoms.

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All compounds are molecules, but not all molecules are compounds

What is a molecule?

• A molecule must contain 2 or more atoms different or the same.

Molecules are the smallest parts of a substance that still retain the properties of that substance

• Note: A compound is always a molecule, but a molecule is not always a compound. Elements can be molecules, but not always. Individual atoms are not molecules.
• Molecules of elements -   H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂, P₄, S₈
•     Molecules of compounds - Na₂O, KOH, CaSO₄, HBr, H₂CO₃

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PURE SUBSTANCES consist of the same type of MOLECULE

• All of the below are pure substances because all of the molecules are the same. Note that compounds are pure substances – it doesn’t matter that not all of the atoms are the same element!

MIXTURES consist of the DIFFERENT TYPES of MOLECULES

• All of the below are MIXTURES because the molecules are NOT the same. Note that mixtures can consist of elements – they don’t have to consist of compounds!

Other terms used

• Monatomic- One atom– (Ag)
• Diatomic – 2 atoms (N­­_2, O_2, F_2, H_2, CO)
• Triatomic – 3 atoms (H­₂O, O₃₎

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Mixtures

• A combination of 2 or more different substances not bonded together. All mixtures can be broken down or separated by physical means. Mixtures are not pure substances.

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• Homogeneous- Uniform throughout. The same throughout. Example: Milk, lemonade, Gatorade, Air
• Heterogeneous- Not uniform throughout. Different throughout. Example: Oil and vinegar, dirty water.

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Suspension: a mixture in which particles of a material are dispersed throughout a liquid or gas but are large enough that they settle out.

Colloid: a mixture in which the particles are dispersed throughout but are not heavy enough to settle out

Solution: A homogenous mixture that appears to be a single substance but is composed of particles of two or more substances that are distributed evenly amongst each other

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MATTER: is either/or

Mixture

Pure Substance

Element

Compound

Homogen-ous

Hetero-geneous

Solution

Colloid

Suspension

metals

Non-metals

Met.oids