2 Atomic SizeAtomic size: the radius of an atom (distance from nucleus to electron cloud) is considered.Measured in angstroms (A) : 1 cm = 1x108 APeriodic Trend: Atomic size within a group increases and decreases as atomic number increases.Atomic size increasesAtomic size increases
3 Ionic SizeSome elements tend to gain or lose electrons to form ions.Metals lose electrons and form positive ions called cations.Nonmetals gain electrons and form negative ions called anions.Fe2+Iron has a 2+ charge (oxidation number) because it lost 2 electons.
4 Ionic Size Periodic Trend: Cations are smaller than original atom. Losing electrons means the nucleus has a greater attraction for electrons remaining.Anions are bigger than original atom. Gaining electrons means the nucleus has less attraction for a greater number of electrons.
5 Learning CheckFor each of the following sets of atoms and ions, decide which is the smallest.a. Na, Na+b. Cl, Cl-c. Na+, Cl-d. H+, H, H-e. Fe2+, Fe3+f. F-, Ne, Na+
7 Octet RuleStates that atoms tend to gain or lose electrons in order to obtain a full set of eight valence electrons to become stable (exception elements in period 1)s and p sublevels are filledEx. Sodium atom, Na ion1s22s22p63s1Fluorine atom, F ion1s22s22p5
8 Ionization energy Energy required to remove an electron from an atom. Measured when element is in gaseous state.First ionization energy: energy required to remove first electron from the highest occupied energy level.Measured in kJ/molSome elements have second, third… ionization energy, meaning they can lose more than one electron forming positive ions.
9 Trends in ionization energy Ionization energy increasesIonization energy increases
10 Trends in ionization energy Ionization energy increases within a period.As the number of protons increases, the nuclear force increases making harder to remove an electron.Ionization energy decreases within a group.As the size of the atom increases, nuclear force has a smaller effect on electrons on highest energy level.Ionization energy increasesIonization energy increases
11 ElectronegativityIs the ability of an element to attract electrons when the atom is in a compound.Noble gases are omitted because they don’t form many compounds.Most electronegative element is FluorineLeast electronegative element is cesium
12 Trends in electronegativity Electronegativity increasesElectronegativity increases