Chemistry Mrs. Partridge Chemical Bonds Chemistry Mrs. Partridge

Chemical Bonding Chemical Bonding – the combination of atoms of elements to form new substances A chemical bond is a force that holds atoms together.                                                     sodium metal +  chlorine gas table salt

The electrons farthest away from the nucleus (valence electrons) play the most significant role in determining how atoms combine.

Octet Rule – atoms with 8 (2 if H or He) are stable; elements with less react with other elements in order to fill their outer shell (valence shell)

There are 2 ways atoms can achieve a noble gas configuration: They transfer electrons They share electrons

Ionic Bonds Ionic bonds are formed when atoms transfer (gain or lose) electrons Because this bond involves the transfer of electrons, one atom gains electrons and the other atom loses electrons

Ionic Bonds When an atom loses an electron, it becomes positively charged – a CATION When an atom gains an electron, it becomes negatively charged – an ANION ION – an atom with a charge

If it isn’t love, what’s going on? Because positives and negatives attract, a bond is formed

The cation is always written first in the formula. Ionic Bonds The cation is always written first in the formula.

Ionic Bonds Ionic bonds occur between a metal and a nonmetal, or involve a polyatomic ion. Polyatomic ions – a group of atoms that together have a charge and function as a single unit

Ionic Bonds Ionization Energy – the amount of energy needed to completely remove an electron from an atom or ion 1st electron held the least tight 2nd electron harder to remove Electron Affinity – name given to the energy change that occurs when an electron is added to an atom or ion Halogens have the highest electron affinity because they only need 1 electron

Oxidation Numbers can predict how atoms will combine. Ionic Bonds Oxidation Numbers can predict how atoms will combine. We’ll use the criss-cross method for ionic compounds. First check for opposite charges – opposites attract Mg+2 Cl-1 Place the cation first Criss-cross the number – it becomes a subscript Mg+2 Cl-1  MgCl2 A one is implied, do not write it as a subscript

Covalent Bonds Covalent bonds are formed when atoms share electrons to fill their outer shells.

Covalent Bonds The positively charged nucleus of each atom simultaneously attracts the negatively charged electrons that are being shared. The electrons spend most of the time between the atoms. The attraction between the nucleus and the shared electrons holds the atoms together.

Covalent Bonds

Covalent Bonds Non-metallic atoms form covalent bonds in units called MOLECULAR COMPOUNDS Diatomic elements – covalent bonds between 2 atoms of the same element (H, Cl, O, F, Br, I, N)

Covalent Bonds Double bonds consist of 2 pairs (4 e-) of electrons being shared Triple bonds consist of 3 pairs (6 e-) of electrons being shared The more pairs of electron shared the shorter and stronger the covalent bond

Covalent Bonds Electronegativity – a periodic property; the attractive force an atom exerts on shared electrons in a chemical bond When electrons aren’t shared equally, the bond is POLAR

Covalent Bonds Polarity – the measurement of inequality in distribution of bonding electrons. Polarity is calculated using the difference between the electronegativities of the atoms. The higher the electronegativity the greater the attraction for the electron. Electronegativity Difference Bond Type 0 – 0.5 Covalent or slightly polar covalent 0.5 – 1.7 Polar covalent > 1.7 Ionic

Metallic Bonds Metallic bonds form between atoms of metals. The outer electrons of the atoms form a common electron cloud. Metal crystals form when atoms crowd together and the outer-level orbitals overlap. Electrons delocalized – electons move easily form atom to atom; they aren’t held in a specific “locality”

The End!