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KEY CONCEPT All living things are based on atoms and their interactions.

KEY CONCEPT All living things are based on atoms and their interactions. H. O. Living things consist of atoms of different elements. An atom is the smallest basic unit of matter. Millions of atoms would fit into a space the size of a period at the end of this sentence.

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KEY CONCEPT All living things are based on atoms and their interactions.

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  1. KEY CONCEPTAll living things are based on atoms and their interactions.

  2. H O Living things consist of atoms of different elements. • An atom is the smallest basic unit of matter. Millions of atoms would fit into a space the size of a period at the end of this sentence. • An element is one type of atom. • The human body has 6 major elements: C, H, O, N, Ca, P and 22 other elements in trace amounts: K, Na, Cl, Mg, S, B, Cr, Co, F, I, Fe etc… Hydrogen atom (H) Oxygen atom (O)

  3. Oxygen atom (O) outermost energy level: 6 electrons (-) Nucleus:8 protons (+)8 neutrons inner energy level: 2 electrons (-) • An atom has a nucleus and electrons. • The nucleus has protons and neutrons. • Electrons are in energy levels outside nucleus. • Electrons are arranged in energy levels based on the octet rule.

  4. Representing Atoms • The exact positions of the electrons cannot be known. They are somewhere in a three-dimensional electron cloud around the nucleus similar to the model shown at the right. Apply: How many electrons would need to be added to fill the outermost energy level of hydrogen? Of oxygen?

  5. _ O H H + + • A compound is made of atoms of different elements bonded together. • water (H2O)

  6. A compound is made of atoms of different elements bonded together. • carbon dioxide (CO2) • water (H2O)

  7. A compound is made of atoms of different elements bonded together. • many other carbon-based compounds in living things • water (H2O) • carbon dioxide (CO2) Contrast: How are elements different from compounds?

  8. gained electron Na loses anelectron to CI ionic bond Sodium atom (Na) Chlorine atom (CI) Sodium ion (Na+) Chloride ion (CI-) Ions form when atoms gain or lose electrons. • An ion is an atom that has gained or lost one or more electrons. • positive ions – called cations • negative ions – called anions • Ionic bonds form between oppositely charged ions. This bond forms between a metal and a non-metal.

  9. Check for understanding: • Why is the sodium ion shown smaller than the sodium atom? • How does the size of the chlorine atom compare with the size of the chloride ion? • What determines whether an atoms becomes a positive or a negative ion?

  10. covalent bonds Oxygen atom (O) Carbon atom (C) Oxygen atom (O) Carbon dioxide (CO2 ) Atoms share pairs of electrons in covalent bonds. • A covalent bond forms when atoms share a pair of electrons. These form when a non-metal is bonded to a non-metal. • multiple covalent bonds • diatomic molecules (there are 7): H, N, O, F, Cl, Br, I

  11. Check your understanding: • How many electrons does a single oxygen atom have in its outer energy level? A carbon atom? • What is the significance of the number of electrons in the outer most energy levels of oxygen and carbon in a molecule of carbon dioxide? • What happens to electrons in outer energy levels when two atoms form a covalent bond?

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