5.4 Trends In the periodic Table (Page 207-210)

Homework: Page 211 # 2-4

Key Concepts (Page 211)

• There are trends, or regular changes, in properties of the elements in the periodic table.

• The arrangement of the electrons in the atoms of elements influences these trends in properties.

• The electrons in the outer energy level of an atom, called the valence electrons, help to determine many properties of the elements.

• The number of valence electrons in an atom is the same in a group but increases as you move across a period.

• The noble gases are non-reactive because they have a full set of valence electrons.

• Their reactivity of other elements is based on their tendency to gain, lose or share electrons to achieve a full set of valence electrons.

• The size of an atom increases as you move down a group in the periodic table.

• The size of an atom also increases as you move from right to left across a row in the periodic table.

1. What is a valence electron? What are the valence electrons of the

elements in Groups 1, 2, 17 & 18?• A valence electron is an electron in the

outermost occupied energy level (shell) of an atom

• Group 1 – 1 valence electron• Group 2 – 2 valence electrons• Group 17 – 7 valence electrons• Group 18 – 2 valence/8 valence electrons

2. What happens with the valence electron/s when a chemical reaction

takes place?• During a chemical reaction, one atom

can join with another atom by gaining, losing or sharing valence electrons.

Chemical Families are groups of elements in the same vertical column. They tend to have similar chemical properties.

The Four Chemical Families: • The Alkali Metals:

• One Electron Beyond Stability – Group 1

• The Alkaline-Earth Metals: • Two Electrons Beyond Stability – Group 2

• The Halogens: • One Electron Short of Stability – Group 17

• The Noble Gases: • A Stable Outer Shell – Group 18

3. What is the trend in the size of the atoms as you move across a period?

What is the trend as you move down a group?

• Atomic size increases across a period, from right to left, and down a group in the periodic table.

4. Based on Figure 5.25, which is the larger: an atom of oxygen or an atom of

sulphur? Explain.• An atom of sulphur is larger than an atom of

oxygen. • As you move down a group, the elements have

valence electrons that occupy higher and higher energy levels.

• The higher the energy level is, the farther the valence electrons are from the nucleus and the larger the atom is.

5. Which is more reactive? Magnesium or calcium? Explain.

• The farther the valence electrons are from the nucleus, the more easily they can be lost and, therefore, the more reactive the element is

• Therefore, calcium is more reactive than magnesium

• Calcium has 2 valence electrons in the 4th energy level and magnesium has 2 valence electrons in the 3rd energy level

• A calcium atom loses its valence electrons more easily than a magnesium atom does, making it more reactive than magnesium

6. In the example of potassium and sodium, why is the larger atom

more reactive?• A potassium atom (larger atom) loses its

valence electron more easily than a sodium atom does, so potassium is more reactive than sodium

HALOGENS

ALKALINE EARTH METALS

ACTINIDES LANTHANIDES

NOBLE GASES

TRANSITION METALS

ALKALI METALS