Chemical Bonding

Chemical Bonding Sections 1-3 Pages 4-21

Combining Atoms through Chemical Bonding • Chemical Bonding: joining of atoms to form new substances. • Properties of these new substances are different from the original elements • An interaction that holds two atoms together is called a chemical bond. • When a chemical bond forms, electrons are shared, gained or lost.

Electron Number and Organization • Electrons organized in energy levels (orbits, clouds, shells) • Atomic number tells you how many electrons (and protons) • Atoms form bonds using electrons in outermost energy level. An electron in the outmost energy level is a valence electron.

Valence Electrons and the Periodic Table • Elements are grouped according to their properties and have the same number of valence electrons. • Most groups (1, 2, 3-18) all have a way to determine their number of valence electrons based on their group number (except Helium)

To Bond or Not to Bond? • Valence electrons determine if an atom bonds. • Group 18 usually does not bond because their outer shell is full because it has 8 electrons. Octet rule. • Atoms gain, lose or share electrons to obtain a full outer shell.

Forming Ionic Bonds • An ionic bond is a bond that forms when electrons are transferred from one atom to another. • During ionic bonding, one or more electrons are transferred from one atom to another to fill that atom’s outer level. • Usually metals.

Ions (forming charged particles) • Positive Ions (lose an electron) • Groups 1 and 2 (metals) • Energy needed • Symbol has a + (ex. Na⁺ or Ca²⁺) • Negative Ions (gain an electron) • Groups 16 and 17 (non metals) • Energy gained • Symbol has a - (ex. Cl⁻ or O²⁻)

Ionic Compounds • When ionic bonds form the charge becomes neutral. • They form a crystal lattice (orderly 3D pattern) which gives the compound certain properties (brittleness, high melting points and high boiling points)

Covalent Bonds • Substances with covalent bonds tend to have low melting and boiling points and are brittle when in solid state • Covalent bond forms when atoms share one or more pairs of electrons • If two nonmetal atoms were to lose electrons it would require a lot of energy, so the two nonmetal atoms don’t transfer electrons…they share instead. • When they share equally they are called Nonpolar covalent bonds. NO charge. • When they share unequally they are called polar covalent bonds. Slight charge. • Usually nonmetals.

Covalent Bonds and Molecules • The force that holds atoms together in a covalent bond is the attraction of each atom’s nucleus for the shared pair of electrons. • A molecule usually consists of two or more atoms joined in a definite ratio

Using Electron Dot Diagrams • An electron dot diagram is a model that shows only the valence electrons. • Write the symbol, then place one dot around the symbol for every valence electron. • Place the first 4 dots alone on each side, then pair up any remaining dots.

Simple Molecules- Diatomic Molecules • Diatomic Molecules:molecules made up of two atoms of the same element • Diatomic Elements: elements that are found in nature as diatomic molecules • Examples: H, O, N, and the Halogens

Metallic Bonds • A metallic bond is a bond formed by the attraction between positively charged metal ions and the electron in the metal • Positively charged metal ions form when metal atoms lose electrons. • The positive metal ions are in fixed position in the metal. • The negative electrons are free to move. • This allows metals these properties of malleability, ductility and electrical conductivity.

Types of Chemical Bonds

Bonding Animation • http://www.bsc2.ehb-schweiz2.ch/Chemie/Simulationen%20Chemie/Bindung/Bindung%20Hundeanalogie.htm

Chemical Bonding