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CHAPTER 6 – CHEMISTRY

CHAPTER 6 – CHEMISTRY. 6.1 Atoms and Their Interactions. Earth supports an enormous variety of organisms. The laws of chemistry govern the structure & function of all living things. Section Objectives: Define element, atom, compound, and molecule. Draw a model of the structure of an atom.

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CHAPTER 6 – CHEMISTRY

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  1. CHAPTER 6 – CHEMISTRY 6.1 Atoms and Their Interactions

  2. Earth supports an enormous variety of organisms. The laws of chemistry govern the structure & function of all living things. • Section Objectives: • Define element, atom, compound, and molecule. • Draw a model of the structure of an atom. • Explain what determines an atom’s stability. • Contrast ionic and covalent bonds.

  3. MATTER • Matter is • Anything that occupies space and has mass. • Mass is • The amount of matter an object has. • Weight is • The force produced by gravity acting on mass. • The same mass would have less weight on the moon because the moon exerts less force (gravity) on the object than the Earth does.

  4. ELEMENTS • Elements are • Pure substances that can’t be broken down into more simple kinds of matter. • Information about the elements is summarized on a chart (back of the room) known as the periodic table of elements. • Each element is represented by a chemical symbol, made of 1, 2 or 3 letters. • In most cases, the symbol comes from the 1st letter or other letters in the name of the element. • Others come from the Latin names of elements, i.e., Na from the Latin word natrium.

  5. ATOMS • Atoms are • The simplest particle of an element that retains all of the element’s properties. • Parts of an ATOM • Nucleus • Proton • Neutron • Electron

  6. NUCLEUS • Is found in the central region of the atom • Makes up the majority of the bulk of the atom • Is made of two subatomic particles • Proton (+) • Atomic number of the element • Neutron (no charge) • Mass number is the total of protons and neutrons of the atom.

  7. ELECTRONS • Small, negatively charged particles in an atom • The number of electrons must = the number of protons in an atom of the same element. • The net electrical charge of an atom = zero. • They are high-energy particles with very little mass.

  8. ELECTRONS, CONT’D… • Electrons move about the nucleus at very high speeds. • They are located in orbitals. • Orbital rules for biology… • First energy level = 2 e- • Second energy level = 8 e- • Third energy level = 8 e- • The technical rules for orbitals will be covered in chemistry next year.

  9. ISOTOPES • Isotopes are atoms of the same element that have a different number of neutrons. • Additional neutrons change the mass of the element. • Most elements are made up of a mixture of isotopes. • Average atomic mass of an element takes into account the relative amounts of each isotope in the element. • The average is the mass found in the periodic table.

  10. COMPOUNDS • Under natural conditions, most elements do not exist alone. • Instead, they combine to form compounds. • Chemical formula: shows the kinds and proportions of atoms of each element that forms a particular compound. • H2O = 2-H; 1-O

  11. COMPOUNDS, CONT’D… • How elements combine to form compounds depends on the number and arrangement of electrons in their orbitals. • An atom is chemically stable when its highest orbital (the one farthest from the nucleus) is filled with the maximum number of electrons.

  12. COMPOUNDS, CONT’D… • Most atoms aren’t stable in their natural state. • They tend to react with other atoms in different ways to become more stable. • Carbon, nitrogen, and oxygen atoms have unfilled orbitals at their highest energy levels (orbitals). • Chemical bonds are the attractive forces that hold atoms together. • Most elements interact with other atoms to form chemical bonds.

  13. COVALENT BONDS • Forms when two atoms share one or more pairs of electrons. • H2O = held together by covalent bonds • Molecule = the simplest part of a substance that retains all of the properties of that substance, and can exist in a free state. • i.e., one molecule of the compound water is H2O.

  14. IONIC BONDS • Figure 2.4, p. 34 • 1. Sodium and chlorine atoms have unfilled outer orbitals. • Because of this, they are reactive. • In order to achieve stability, the outer e- of the Na atom is transferred to the Cl atom. • This makes sodium slightly positive. (Na+) • This makes both atoms more stable than they were before.

  15. IONIC BONDS, CONT’D… • 2. The chlorine that has gained an electron from sodium now has 8 e- in it’s outer orbital. It is stable. • With this additional e- chlorine is slightly negative. • Cl- • Both Na+ and Cl- have a charge. • This makes them ions. • An ion is an atom or molecule with an electrical charge.

  16. Ionic Bonds, cont’d… • 3. Positive and negative electrical charges attract. • Na+ and Cl- are attracted to each other and form the ionic compound NaCl. • Table salt

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