1. Periodic Trends

2. Atomic Radius
Defined as half of the distance between two bonding atoms nuclei (since electrons do not have a clearly defined edge)

3. Atomic Radius Across a Period
Atomic radius generally decreases in size as you move left to right across the period
Increasing positive charge in the nucleus pulls the electrons of the same energy level in.

4. Atomic Radius Down a Group
Atomic radius increases as you move down a group
Orbital size increases as you move down a group with increasing energy level
Larger orbitals means that outer electrons are farther from the nucleus. This increased distance offsets the greater pull of the increased nuclear charge.
As additional orbitals between the nucleus and the outer electrons are occupied, the inner electrons shield the outer electrons from the pull of the nucleus this is called shielding.

5. Shielding
The inner electrons shield the outer electrons from feeling the pull of the nucleus

7. Cation and Anion
An ion is a positively or negatively charged atom that gains or loses an electron.
A cation loses electrons and produces a positive charge
An anion gains electrons and produces a negative charge

8. Ionic Radius - Cations
Groups 1A, 2A, 3A, and other metals lose electrons and form cations.
When atoms lose electrons they become smaller
The electron lost will be a valence electron leaving a completely empty outer orbital
Protons in nucleus can pull fewer electrons tighter

9. Cation Atom 12 electrons 10 electrons Mg2+ Mg Magnesium Cation
12 protons
12 electrons
12 protons
10 electrons
Mg2+
Magnesium Cation Mg
Magnesium Atom

10. These atoms lost electrons and became smaller cations.

11. Ionic Radius - Anions
Group 5A, 6A, and 7A tend to gain electrons and form anions
When atoms gain electrons and form negatively charged ions, they become larger.
Protons in nucleus have more electrons to pull and cannot pull in as tight

12. Anion Atom 18 electrons 16 electrons S Sulfur Atom S2- Sulfer Anion 16
protons
18 electrons
16 protons
16 electrons S
Sulfur Atom
S2-
Sulfer Anion

13. These atoms gained electrons and became larger anions

14. Ionization Energy
The energy required to remove an electron from a gaseous atom
Indication of how strongly an atom’s nucleus holds onto its valence electron
Groups 1A, 2A, and 3A tend to have low ionization energies because they want to lose electrons.

15. Ionization Energy Trends – Across a Period
Ionization energy generally increases as you move left to right
Across a period electrons are added to the same energy level (same distance away from the nucleus), yet the nuclear charge is increasing across a period increasing the attraction to the electrons.

16. Ionization Energy Trends – Down a Group
Ionization energy decreases as you move down a group
Down a group electrons are added to a higher energy level (farther distance away from the nucleus), making it easier to remove an electron

18. Octet Rule Sodium atom 1s22s22p63s1
Sodium ion 1s22s22p6 (Sodium atom lost 1 electron)
Neon 1s22s22p6
Sodium ion has the same electron configuration as neon
Octet rule states that atoms gain, lose, or share electrons to acquire a full set of eight valence electrons (to be like a noble gas)

19. Electronegativity
Indicates an element’s ability to attract electrons in a shared chemical bond
fluorine (F) is the most electronegative element
cesium (Cs) and francium (Fr)are the least electronegative
Noble gases do not tend to have an electronegativity number since they tend not to form compounds

20. Trends with Electronegativity
Electronegativity increases as you move left-to-right across a period
Electronegativity decreases as you move down a group