Ionic and Metallic Bonding Chapter 7

WHAT IS AN ION? An atom or groups of atoms that has a positive or negative charge.

Ions Valence electrons- electrons in the highest occupied energy level. To find: look at group #. Electron dot structure- shows valence electrons as dots. Octet rule- atoms tend to reach the electron configuration of a noble gas.(8 dots) Atoms lose valence electrons produces a positive charge.(cation) Na The gain of electrons-anion Cl -ide ending Chloride is a halide ion

Ionic bond and Ionic compound Ionic bond- anions and cations have opposite charges and attract one another. Properties of an ionic compound- crystalline solids at room temperature. High melting points. Conduct electricity when melted and dissolved in water.

Bonding in metals Metallic bonds- attraction of the free floating valence electrons for the positively charged metal ions. Metal ions are arranged in very tight orderly patterns. Alloys: mixtures composed of two or more elements, at least one of each metal. Alloys are important because their properties are often superior to those of their component element.

Chapter 8 Covalent bonding

Molecules and Molecular Compounds Covalent bonds- atoms held together by joined electrons. A molecule is a neutral group of atoms joined together by covalent bonds. Molecular Compound-compound that is composed of molecules. Molecular compounds tend to have relatively lower melting and boiling points than ionic compounds.

Molecular Formulas A molecular formula is the chemical formula of a molecular compound. A molecular formula shows how many atoms of each element a molecule contains. The molecular formula for ethane is C 2 H 6

Covalent Bonding Octet Rule- In covalent bonds, electron sharing usually occurs so that atoms attain the electron configurations of noble gases. single covalent bond- a bond formed when two atoms share a pair of electrons. An electron dot structure represents the shared pair of electrons with dots. H:H

Double and Triple Covalent bonds Unshared pair- valence electrons that is not shared between atoms. Triple bond-share three electron pairs. Atoms form double or triple covalent bonds if they can attain a noble gas structure by sharing two or three pairs of electrons. Double bond –share two electron pairs

Coordinate Covalent Bonds In a coordinate covalent bond the shared electron pair comes from one of the bonding atoms.

Bond Dissociation Energies Bond dissociation energy- the energy required to break the bond between two covalently bonded atoms. A large bond dissociation energy corresponds to a strong covalent bond. Resonance The actual bonding of oxygen atoms in ozone is a hybrid, or mixture, of extremes represented by the resonance forms. Resonance structure- occurs when it is possible to draw two or more valid electron dot structures that have the same number of electron pairs for a molecules or ions.

Bonding Theories Molecular orbitals- orbitals that apply to the entire molecule. Bonding orbital- a molecular orbital that can be occupied by two electrons of a covalent bond. Sigma bond Very strong bond. Pi bond Week bond.

VSEPR Theory Explains the three- dimensional shape of methane. SHAPES: Bent shape Pyramidal shape Tetrahedral shape Hybrid orbitals Orbital hybridization provides info about molecular bonding and molecular shapes.

Polar bonds Nonpolar covalent bonds- atoms in the bond pull equally. Polar bond- electrons between atoms aren't shared equally. The more electronegative atoms attract electrons more strongly and gains a slightly negative charge. The less electronegative atom has a slightly positive charge. Polar molecules- on end of the molecule is slightly negative the other end is slightly positive. A molecule that has two poles is called a dipole. When polar molecules are placed between opposite charged plates, they tend to become oriented with respect to the positive and negative plates.

The two weakest attractions between molecules. Van der Waals forces consist of dipole interactions and dispersion forces. Dipole interactions occur when polar molecules are attracted to one another. Dispersion forces, the weakest of all molecular interactions, are caused by the motion of electrons. They occur even between non-polar molecules. Hydrogen bond very strong bond! Van der Waals Forces