Regents Biology The Chemical Basis of Life Sections 2.6 – 2.9 Chemical Bonding Today we will learn about how atoms bond together

Regents Biology Review Atomic Strucutre

Regents Biology Chemical Bonding Properties  Bonds are made with electrons  electrons determine chemical “behavior” of atom  depends on number of electrons in atom’s outermost shell  valence electrons How many valence electrons do you see? How many valence electrons do you see?

Regents Biology Elements & their valence shells Elements in the same row have the same number of shells Moving from left to right, each element has a sequential addition of electrons (& protons)

Regents Biology Elements & their valence shells Elements in the same column have the same valence & similar chemical properties

Regents Biology Bonding Properties  Effect of electrons  Atoms like to have maximum number of valence electrons!!!!! What’s the magic number? How does this atom behave?

Regents Biology – – – Chemical Reactivity  So atoms tend to complete a partially filled valence shell or empty a partially filled valence shell This tendency drives chemical reactions… and creates bonds

Regents Biology Chemical Reactivity Quiz

Regents Biology – – H 2 (hydrogen gas) Covalent bond Bonds in Biology  Ionic Bonds (atoms to ions)  Covalent Bonds (shares e - )  nonpolar & polar  Hydrogen Bonds Hydrogen bond H2OH2O H2OH2O Ionic bond

Regents Biology LE 2-7a-1 Transfer of electron Na Sodium atom Cl Chlorine atom Ionic Bonds Ion – any atom that has lost or gained an electron.

Regents Biology LE 2-7a-2 Na  Sodium ion Cl  Chloride ion Sodium chloride (NaCl) Ionic Bonds

Regents Biology Na  Cl 

Regents Biology Covalent bonds  Covalent bonds are strong bonds  two atoms share a pair of electrons  both atoms holding onto the electrons  very stable  Forms molecules – – H 2 (hydrogen gas) H — H H 2 O (water) H H Oxygen H H O

Regents Biology Multiple covalent bonds  2 atoms can share >1 pair of electrons  double bonds  2 pairs of electrons  triple bonds  3 pairs of electrons  Very strong bonds H H–C–H H – – More is better!

Regents Biology Nonpolar covalent bonds  Pair of electrons shared equally by 2 atoms  example: methane (CH 4 ) H H–C–H H – –

Regents Biology H H Oxygen Polar covalent bonds  Pair of electrons shared unequally by 2 atoms  example: water = H 2 O  oxygen has stronger “attraction” for the electrons than hydrogen  water is a polar molecule + + – – – –

Regents Biology Covalent Bond A water molecule

Regents Biology Penguins gone bad! Any Questions?