Covalent bonds Pg

Covalent Bonds G Nonmetals with high ionization energies do not tend to form ionic bonds (transfer of electrons) G Instead of transferring electrons they share them G Nonmetals with high ionization energies do not tend to form ionic bonds (transfer of electrons) G Instead of transferring electrons they share them

Sharing Electrons G Two atoms of hydrogen can share their electrons to achieve a stable electron configuration. G Covalent Bond - a chemical bond in which two atoms share a pair of valence electrons

Molecular Models G The electron cloud model and space-filling model show that orbitals of atoms overlap when a covalent bond forms

Molecules of elements G Molecule - a neutral group of atoms that are joined together by one or more covalent bonds G They are neutral because the number of protons and electrons are balanced in the shared molecule G The attractions between the shared electrons and the protons in each nucleus hold the atoms together in a covalent bond

Molecules of elements G Many nonmetal elements exist as diatomic molecules G Diatomic means “two atoms” G Many nonmetal elements exist as diatomic molecules G Diatomic means “two atoms”

Multiple Covalent Bonds G A Nitrogen molecule (N 2 ) shares three pairs of electrons, each atom then has eight valence electrons G Each pair of shared electrons is represented by a long dash in the structural formula G When two atoms share three pairs of electrons it is called a triple bond G When two atoms share two pairs of electrons it is called a double bond

Unequal Sharing of Electrons G In general, elements on the right of the periodic table have a greater attraction for electrons than elements on the left (except noble gases) G And elements at the top of a group have a greater attraction for electrons than elements at the bottom of a group G In general, elements on the right of the periodic table have a greater attraction for electrons than elements on the left (except noble gases) G And elements at the top of a group have a greater attraction for electrons than elements at the bottom of a group

Polar Covalent Bonds G When hydrogen and chlorine form a covalent bond the chlorine atom has a greater attraction for the electrons than the hydrogen atom G In the hydrogen chloride molecule, the shared electrons spend more time near the chlorine atom than near the hydrogen atom G Polar covalent bond- a covalent bond in which electrons are not shared equally G When atoms form a polar covalent bond, the atom with the greater attraction for electrons has a partial negative charge. The other atom has a partial positive charge

Hydrogen chloride

Polar and Nonpolar Molecules G If a molecule with a polar covalent bond contains only two atoms, it will be polar G But when molecules have more than two atoms, the answer is not as obvious G The type of atoms in a molecule and its shape are factors that determine whether a molecule is polar or nonpolar Polar Nonpolar

Carbon dioxide (CO 2 ) G Each double bond in carbon dioxide is polar because oxygen has a grater attraction for electrons than the carbon atom G Because the molecule is linear (all three atoms line up in a row) the pull of the charges cancel out and the molecule as a whole is nonpolar G Each double bond in carbon dioxide is polar because oxygen has a grater attraction for electrons than the carbon atom G Because the molecule is linear (all three atoms line up in a row) the pull of the charges cancel out and the molecule as a whole is nonpolar

Water (H 2 0) G Water molecule has two single bonds which are polar because oxygen has a greater attraction for electrons that hydrogen G The water molecule has a bent shape so the polar bonds do not cancel out G The two hydrogen atoms are located on the same side of the molecule opposite the oxygen atom G The oxygen side has a partial negative charge and the hydrogen side has a partial positive charge

Attraction Between Molecules G Attractions between polar molecules are stronger than attractions between nonpolar molecules G Water boils at C and Methane boils at C even if they are very similar in mass G Because water molecules are polar, the attractions between the molecules are stronger than the attractions between the nonpolar methane molecules G Attractions between nonpolar molecules exist but they are just weaker G Attractions among nonpolar molecules explain why nitrogen can be stored as a liquid at low temperatures and high pressures. G Attractions between polar molecules are stronger than attractions between nonpolar molecules G Water boils at C and Methane boils at C even if they are very similar in mass G Because water molecules are polar, the attractions between the molecules are stronger than the attractions between the nonpolar methane molecules G Attractions between nonpolar molecules exist but they are just weaker G Attractions among nonpolar molecules explain why nitrogen can be stored as a liquid at low temperatures and high pressures.