3Atomic RadiusMeasures as distance from nucleus to nucleus and divided by 2.Unit commonly used is pmpicometer= 10-12mExample: iodine atomic radius 140pm
4How does atomic radius change across a period? It is smaller to the right.Why?More protons in the nucleus higher electrical force pulls electrons closer to nucleus.
5How does atomic radius change down a group? It is larger down the group.Why?Valence electrons are at higher energy levels and are not bound as tightly to the nucleus because they are screened or shielded ( pushed away) by other electrons in inner levels.
6NoteThere are some exceptions. Example column 13.
11Ionization energyIonization energy is the amount of energy needed to remove an electron from a gaseous atom.First ionization energy –Second ionization energy –
12Ion Positive ion ---removal of electron Negative ion--- addition of electron
13How does ionization energy change down a group? The first ionization energy decreases as you move down a group.Why?The size of the atom increases.Electron is further from the nucleus.
14How does ionization energy change across a period? The first ionization energy increases as you move from left to right across a period.Why?Nuclear charge increases while shielding is constant.Attraction of the electron to the nucleus increases.
16Ionic size Metallic elements easily lose electrons. Non-metals more readily gain electrons.How does losing or gaining an electron effect the size of the atom (ion) ?
17Positive ionsPositive ions are always smaller that the neutral atom. Loss of outer shell electrons.
18Negative IonsNegative ions are always larger than the neutral atom. Gaining electrons.
19Ion size trends in periods. Going from left to right there is a decrease in size of positive ions.Starting with group 5, there is sharp increase followed by a decrease in the size of the anion as you move from left to right.
20Ion size trends in columns. Ion size increases as you move down a column for both positive and negative ions
21Electronegativity: the ability of an atom in a bond to pull on the electron. (Linus Pauling)
22ElectronegativityWhen electrons are shared by two atoms a covalent bond is formed.When the atoms are the same they pull on the electrons equally. Example, H-H.When the atoms are different, the atoms pull on the electrons unevenly. Example, HCl
23Trends in Electronegativity Electronegativity generally decreases as you move down a group.Electronegativity of the representative elements (Group A elements) increases as you move across a period.
24Electronegativities of Some Elements Element Pauling scaleFClONSCHNaCs 0.7
25Note Most electronegative element is F (EN 4.0) Least electronegative stable element is Cs(EN 0.7)
26Summary Ionization energy decreases Electronegativity decreases Nuclear charge increasesAtomic radius increasesShielding increasesIonic size increasesShielding is constantAtomic Radius decreasesIonization energy increasesElectronegativity increasesNuclear charge increases