1. Elements, Compounds, Bonds
Matter
How is it organized?

2. Elements, Atoms & Compounds
Element: simplest type of matter with unique chemical properties
92 elements occur naturally
Atom: Smallest particle of an element that has the chemical characteristics of that element
Compound: Substance containing two or more elements in a fixed ratio

3. Atoms Composed of three subatomic particles:
protons (+) & neutrons (0) make up the nucleus
electrons (-, e-) in orbitals (clouds)

4. Periodic Table

5. Atoms Mass of atom = summed mass of its protons and neutrons
1 proton = 1 atomic mass unit or amu
1 neutron ~1 amu
Mass = Atomic weight

6. Approximate atom Pea = nucleus electron (-) proton (+) nucleus
neutron (0)

7. Atoms Stable atoms always have same # protons. # protons = atomic #
Carbon [C] = 6
Atoms can have differing #’s of neutrons. # protons + # neutrons = Atomic weight (mass number)
12C has 6 protons and 6 neutrons
13C has 6 protons and 7 neutrons

8. Periodic Table

9. Importance (by weight)

10. Valence and reactivity
2 electrons
Remember: electrons are arranged in valence shells or energy levels that “orbit” the nucleus.
# of electrons in atoms influence their reactivity, relative to other atoms.
2 electrons
8 electrons

11. Atoms with unfilled electron shells are reactive…
Atoms are “greedy” (want full e- orbitals) and “lazy” (don’t want to work hard to achieve them)
Results in formation of chemical bonds
Three types of bonds
Ionic bonds
Covalent bonds
Hydrogen bonds

12. Ionic bonds
Ionic bonds form between anions (atoms that stripped an e- from another atom) and cations (atoms that lost an e-)
Salts form by ionic bonding
Basically, a strong electrostatic attraction

13. Covalent bonds Covalent bonds form when atoms share e-.
Single or double
H-H (H2)
O=C=O (CO2)
# of bonds formed = # of e- needed to fill outer shell

14. Non-polar Covalent bonds
Equal sharing of e-
Nuclei of similar size have similar elecronegativity: pull on shared electrons in a covalent bond

15. Polar Covalent bonds Form due to unequal sharing of e-
Relative size and electrical attraction of nuclei differ
Partial + and partial – sides of molecule result

16. Hydrogen bonds
Weak attraction between opposite charged poles of polar molecules
IMPORTANT bond
determines structure of large, complex molecules
Produces cohesion (water droplets)

17. Hydrogen bonds give H20 it’s amazing properties

18. Structural bonds Responsible for secondary structure of proteins
-helix
-pleated sheet

19. Allow water transport
H-bonding creates surface tension between water molecules
As H20 evaporates, it pulls “attached” H20 molecules along with it

20. Ionic & covalent bonds form:
Molecules: atoms held together by covalent bonds
H20, O2, H2, CO2
Compounds: chemical substance made of atoms of 2 or more elements, regardless of type of bond joining them.
H20, NaCl, CO2.

21. Concept Check
The reactive properties or chemical behavior of an atom mostly depend on the number of
the electrons in each electron shell of the atom.
the neutrons found in the nucleus.
the filled electron shells.
the electrons in the outer electron shell of the atom.
Answer: 4

22. Answer
The reactive properties or chemical behavior of an atom mostly depend on the number of
the electrons in the outer electron shell of the atom.

23. Concept Check Water molecules form hydrogen bonds because
Concept Check
Water molecules form hydrogen bonds because
the water molecule is polar.
the oxygen molecule is positively charged.
the water molecule forms a tetrahedron.
the hydrogen atoms are negatively charged.
Answer: 1

24. Answer Water molecules form hydrogen bonds because
Answer
Water molecules form hydrogen bonds because
the water molecule is polar.