Valence Electrons and ionic Bonding

Valence Electrons and ionic Bonding

Valence Electrons • electrons in the highest occupied energy level • always in the s and p orbitals • normally just a draw a circle to represent these two orbitals • determines the chemical properties of an element • usually the only electrons used in chemical bonds

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Lewis/Electron Dot Diagrams/Structures • electron dot structures/diagrams are used to show valence electrons • each dot around the element symbol represents a valence electron

B is 1s2 2s2 2p1; • 2is the outermost energy level • it contains 3 valence electrons, 2 in the s and 1 in the p • Br is [Ar] 4s2 3d10 4p5How many valence electrons are present?

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Ionic Charge • when forming compounds, atoms tend to achieve the electron configuration of a noble gas (ns2np6) • this means they “want” their highest energy level filled with 8 electrons the easiest way possible • atoms of metallic elements lose electrons producing cations (positive ions) • Ca becomes Ca2+ • atoms of nonmetallic elements gain electrons producing anions (negative ions) • Cl becomes Cl1-

e- + + - -

1+ 2+ 3+ 4+/- 3- 2- 1- 0 As it turns out, atoms bond together for a very simple reason: atoms like to have full valence shells.

for transitional metals, charges of cations may vary • iron can be Fe2+ or Fe3+ • other elements fill some orbitals but don’t quite get a noble gas electron configuration

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Formation of Compounds • usually composed oppositely charged metallic cations and nonmetallic anions • form a compound with overall zero charge • know as the rule of zero charge - anions + cations

Na “gives” Cl one electron and now both atoms have a full valence shell (electron configuration of a noble gas)

Chemical Formula • shows the kinds and numbers of atoms in the lowest whole-number ratio of ions in the ionic compound • Na 1+ + Cl1- NaCl • Ca 2+ + Cl1-  CaCl2 • Mg 2+ + O 2-  MgO

Mg and N? • it takes two nitrogens to combine with three magnesiums • Mg3N2 • magnesium nitride

Al and O

Na 1+ + F 1- NaF

Properties of Ionic Compounds • high melting points • can conduct electric currents when melted or dissolved in water • will shatter if impacted or crushed

Valence Electrons and ionic Bonding