Chapter 12 Chemical Bonding Ionic Bonds Ionic compounds Covalent Bonds Molecular compounds

Ionic Bonds Metals lose electrons forming positive cations alkali metals are +1 alkaline earth metals are +2 transition metals are variable Nonmetals gain electrons forming negative anions halogens are -1 column 16 are -2 column 15 are -3 Noble gases do not gain electrons

Ionic e- Configuration Electrons lost come from the valence electrons. Na 1s22s22p63s1 Na+ 1s22s22p6 Electrons gained are placed in the valence shell to give the nonmetal the same electron configuration as the closest noble gas. F 1s22s22p5 F- 1s22s22p6

Ionic Compounds Cations and anions are attracted due to their opposite electrical charge. They form compounds that balance the charges between the two Na+ + Cl- → NaCl Mg2+ + O2- → MgO Sr2+ + F- → SrF2

Covalent Bonding Many substances in nature are molecular. Molecules are composed of neutral atoms combined together. Unlike ionic compounds, which are formed by oppositely attracted charged atoms, molecules are formed by neutral atoms. These atoms combine by sharing outer electron orbitals [valence e-] to achieve noble gas electron configuration.

Covalent Bonding The simplest molecules are the diatomic elemental substances H2, N2, O2, F2, Br2, I2, Cl2. In the hydrogen molecule, both hydrogen atoms provide a single electron into the s-orbital to achieve a similar electron configuration as helium. This is referred to as a single covalent bond because one pair of electrons are shared.

Covalent Bonding Oxygen has 6 electrons in the valence shell (outer s and p orbitals). 2 electrons are needed to become isoelectronic with Neon. Oxygen supplies the two electrons with its partner supplying two. This is a double covalent bond.

Covalent Bonding Water is a covalently bonded molecule made up of 2 hydrogen and 1 oxygen atoms. The hydrogen atoms provide 1 electron each to the oxygen as well as oxygen sharing an electron to each of the hydrogens.

Unequal Electron Sharing Electronegativity The element’s attractiveness to an electron pair in a covalent bond The values range from 4.0 (Fluorine) to .70 (Francium) The larger the difference between elements in a covalent bond, the more the electrons reside closer to the more electronegative element.

Electronegativity

Bond Polarity A type of covalent bond between two atoms in which electrons are shared unequally. Because of this, one end of the molecule has a slightly negative charge and the other a slightly positive charge.

Dipole Moment When charge is distributed unevenly in a molecule, there will be areas of positive and negative charge. This creates a Dipole Moment in the molecule. The greater the separation of charge, the greater the dipole moment. In general the dipole moment is the ability of the molecule to align itself in an external field.

Dipole Moment Water is a polar molecule with a dipole moment. This fact accounts for the many unique properties of water.

Lewis Dot Structure Notation Lewis Dot structures are a shorthand notation of keeping track of valence electrons available for sharing in covalent bonds. Each dot adjacent to the element symbol represents valence electrons.

Lewis Dot Structures