The Chemical Basis of Life Chapter 4

Matter Anything that occupies space. Anything that occupies space. Composed of one or more chemical elements. Composed of one or more chemical elements.Examples?

Element vs. Compound Element: A pure substance that can not be broken down into other substances by chemical means. Element: A pure substance that can not be broken down into other substances by chemical means. Compound: Composed of two or more elements that are chemically combined in a fixed ratio. Compound: Composed of two or more elements that are chemically combined in a fixed ratio.

4 elements make up 96% of living matter in your body. They are: O – Oxygen H – Hydrogen C – Carbon N – Nitrogen

Examples H2OH2O Iron is an Element: Fe Salt is a compound: NaCl + = Water is a compound:

Different elements have different properties These properties are based on the structure of their atoms. These properties are based on the structure of their atoms.

Atoms Are made up of subatomic particles Are made up of subatomic particles Protons Protons Neutrons Neutrons Electrons Electrons

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Atomic Number The number of protons in an atom The number of protons in an atom All atoms of the same element have the same atomic number. All atoms of the same element have the same atomic number.

Electrons and Reactivity An atom’s electrons determine its reactivity. An atom’s electrons determine its reactivity. There are different energy levels surrounding the nucleus into which electrons are placed. There are different energy levels surrounding the nucleus into which electrons are placed.

1 st Energy Level Closest to the nucleus Closest to the nucleus Holds 2 electrons Holds 2 electrons Holds 8 electrons Holds 8 electrons 2 nd Energy Level

The energy levels closest to the nucleus The energy levels closest to the nucleus Having partially filled energy levels is what makes atoms reactive. Having partially filled energy levels is what makes atoms reactive. Carbon: Carbon:

Draw models for: Neon (10 electrons) Neon (10 electrons) Nitrogen (7 electrons) Nitrogen (7 electrons) Lithium (3 electrons) Lithium (3 electrons) Which atom(s) is/are reactive? Which is/are not as reactive?

Ionic Bonds When an atom transfers an electron to another atom.

Example: Lithium Fluoride (LiF) Lithium Fluoride (LiF) Lithium (3 electrons) + Flourine (9 electrons) Lithium (3 electrons) + Flourine (9 electrons)

Ionic Bonds (continued) When the electron moves from one atom to another, the atoms now become charged (ions). When the electron moves from one atom to another, the atoms now become charged (ions). What are the charges on each atom? What are the charges on each atom? Li (+) Li (+) F (-) F (-) What happens now with these two ions? What happens now with these two ions?

Covalent Bonds When two atoms share electrons When two atoms share electrons Stronger than an ionic bond Stronger than an ionic bond

Structure of Water H & O covalently bonded together. H & O covalently bonded together. Water is polar Water is polar It has a slightly positive charge on one end and a slightly negative charge on the other. It has a slightly positive charge on one end and a slightly negative charge on the other.