Ionic Bonds January 5, th grade Chapter 4.2

Meme Moment

How to Count Valence Electrons Find the element. Focus on that row ( period ). Count s+p spots to get to that element.

Electrons & Stability When an atom has a full set (8) or empty set (0) of valence electrons, it is stable o H, He, Li, Be are OK with just 2 If an atom doesn’t have a full set of valence electrons, it will try to steal, give, or share them with other atoms This makes chemical bonds o Stealing/giving = ionic bond o Sharing = covalent bond When it’s very close to a full set (alkali metal or halogen) it will work extra hard and be very reactive

Ions If an atom wants a full or empty valence set, it can steal or give away electrons If # electrons changes, the number of positive protons & negative electrons won’t match This means that the atom will have an overall charge # protons – # electrons = charge # electrons normally - # electrons now = charge E.g. Sodium gives away 1 electron = +1 charge Could also show 1 – 0 = +1 charge

Ions, part 2 # protons – # electrons = charge # electrons normally - # electrons now = charge Use a Lewis diagram or the periodic table to check how many electrons are needed E.g. Sodium gives away 1 electron = +1 or 1-0=+1 Show whether the charge is + or – Draw the charge to the top right side of the symbol Na + or Na +1 or Na 1+

Practice! Atom How to get a full or empty valence set? MathSymbol Oneeds 2 more6-8= -2O -2 Ca Br K

Ionic Compounds Ions pair up so that the molecule is neutral overall Positive charge written first Na + with Cl - makes NaCl (+1-1=0) Mg +2 with O -2 makes MgO (+2-2=0) If the charges don’t match, use subscripts to balance Mg +2 with Br – makes MgBr 2 (+2 + 2(-1) = 0) Na + with N -3 makes Na 3 N (3(+1) -3 = 0)

Practice! AtomsIonsMathFormula K, OK +, O -2 2(+1)-2=0K2OK2O Ca, Br B, Cl Al, O

Polyatomic Ions FormulaNameCharge NH 4 + ammonium+1 NO 3 - nitrate HCO 3 - bicarbonate CO 3 -2 carbonate-2 SO 4 -2 sulfate-2

Polyatomic Ions in Compounds Treat polyatomic ions like an atom of their own NH 4 + with Cl - makes NH 4 Cl (+1-1=0) Mg +2 with CO 3 -2 makes MgCO 3 (+2-2=0) If the charges don’t match, use subscripts to balance Use parentheses around the polyatomic ion Mg +2 with NO 3 – makes Mg(NO 3 ) 2 (+2 + 2(-1) = 0) NH 4 + with N -3 makes (NH 4 ) 3 N (3(+1) -3 = 0)

Naming Ionic Compounds First word is the first element (the positively-charged ion) Second word is the second element, changed to “ide” Use polyatomic names instead if you have a polyatomic ion MgO is magnesium oxide NH 4 Cl is ammonium chloride KBr is potassium bromide

Practice! Ions Ionic Compound Name NH 4 +, Br - NH 4 Br ammonium bromide Ca +2, NO 3 - Na +, HCO 3 - K +, CO 3 -2 Al +3, SO 4 -2

Properties of Ionic Compounds Conduct electricity when melted or dissolved in water Hard o Na can be cut with a spoon. NaCl can’t Brittle Form crystals High melting point o Na melts at 98°C, but NaCl melts at 801°C

Periodic Table