Elements, Compounds, Bonds Matter How is it organized?

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

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

Periodic Table

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

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

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

Periodic Table

Importance (by weight)

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

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

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

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

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

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

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

Hydrogen bonds give H20 it’s amazing properties

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

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

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.

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

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.

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

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