1. For any representative element its group number equals the number of valance electrons (electrons in the highest occupied energy level)

2. Ions An ion is an atom or group of atoms that has a positive or negative charge Atoms become ions when electrons are lost or gained Atoms can become cations or anions

3. More positively charged protons than negatively charged electrons, the ion has a net positive charge The charge for a cation is written as a number (number of electrons lost) followed by a plus sign Metals tend to form cations Cation (Positively charged atom)

4. Anion (Negatively Charged atom) More negatively charged electrons than positively charged protons, the ion has a net negative charge The charge for an anion is written as a number (number of electrons gained) followed by a minus sign Nonmetals tend to form anions

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6. PERIODIC TRENDS Chapter 6.3

7. Atomic Size The size is expressed as an atomic radius The atomic radius is ½ the distance between the nuclei of two atoms of the same element when the atoms are joined

8. In general, atomic size increases from top to bottom within a group, and decreases from left to right across a period

9. Practice Question.... 1. Which of the following has the smallest atomic radius? Rb, Cs, Sr 2. Order the following atoms in increasing atomic radius (smallest to largest) Rubidium, Gallium, Potassium

10. Ionization Energy Ionization energy is the energy required to remove an electron from an atom Ionization energy tends to decrease from top to bottom within a group and increase from left to right across a period

11. Practice Question... 1. Which of the following elements has the smallest ionization energy Sodium, Calcium, Potassium, Magnesium 2. List the following elements in increasing ionization energy (smallest to largest) Cesium, Bismuth, Oxygen, Beryllium

12. Electronegativity Electronegativity is the ability of an atom to of an element to attract electrons Electronegativity tends to decrease from top to bottom within a group and increase from left to right across a period