Chemical Bonds

Elements, Atoms, and Ions Chemistry I: Chapter 2b Chemistry I Honors: Chapter 3 ICP: Chapter 17

The Language of Chemistry CHEMICAL ELEMENTS - pure substances that cannot be decomposed by ordinary means to other substances. Aluminum Bromine Sodium

The Language of Chemistry The elements, their names, and symbols are given on the PERIODIC TABLE How many elements are there?

The Periodic Table Dmitri Mendeleev (1834 - 1907)

The Atom nucleus (of protons and neutrons) An atom consists of a nucleus (of protons and neutrons) electrons in space about the nucleus. Electron cloud Nucleus

A MOLECULE is the smallest unit of a compound that retains the chemical characteristics of the compound. Composition of molecules is given by a MOLECULAR FORMULA H2O C8H10N4O2 - caffeine

Copper atoms on silica surface. An __Atom___ is the smallest particle of an element that has the chemical properties of the element. Copper atoms on silica surface. Distance across = 1.8 nanometer (1.8 x 10-9 m)

CHEMICAL COMPOUNDS are composed of atoms and so can be decomposed to those atoms. The red compound is composed of • nickel (Ni) (silver) • carbon (C) (black) • hydrogen (H) (white) • oxygen (O) (red) • nitrogen (N) (blue)

Compounds composed of 2 or more elements in a fixed ratio properties differ from those of individual elements EX: table salt (NaCl)

ATOMIC COMPOSITION Protons (p+) Electrons (e-) Neutrons (no) + electrical charge mass = 1.672623 x 10-24 g relative mass = 1.007 atomic mass units (amu) but we can round to 1 Electrons (e-) negative electrical charge relative mass = 0.0005 amu but we can round to 0 Neutrons (no) no electrical charge mass = 1.009 amu but we can round to 1

IONS IONS are atoms or groups of atoms with a positive or negative charge. Taking away an electron from an atom gives a CATION with a positive charge Adding an electron to an atom gives an ANION with a negative charge. To tell the difference between an atom and an ion, look to see if there is a charge in the superscript! Examples: Na+ Ca+2 I- O-2 Na Ca I O

IONIC BOND bond formed between two ions by the transfer of electrons

Ionic Bonds: One Big Greedy Thief Dog!

1). Ionic bond – electron from Na is transferred to Cl, this causes a charge imbalance in each atom. The Na becomes (Na+) and the Cl becomes (Cl-), charged particles or ions.

COVALENT BOND bond formed by the sharing of electrons

Covalent Bond Between nonmetallic elements of similar electronegativity. Formed by sharing electron pairs Stable non-ionizing particles, they are not conductors at any state Examples; O2, CO2, C2H6, H2O, SiC

Covalent Bonds

when electrons are shared equally NONPOLAR COVALENT BONDS when electrons are shared equally H2 or Cl2

2. Covalent bonds- Two atoms share one or more pairs of outer-shell electrons. Oxygen Atom Oxygen Atom Oxygen Molecule (O2)

when electrons are shared but shared unequally POLAR COVALENT BONDS when electrons are shared but shared unequally H2O

Polar Covalent Bonds: Unevenly matched, but willing to share.

- water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.