Key Concept: Families of the Periodic Table

Sample Questions:

1.(JUNE 1996 416/436): Five elements are listed in the first column. The second column lists characteristics for one of these elements. Match each element with the appropriate characteristic

Element

Characteristic

Na

1. Its outermost energy level contains 6 electrons.

Ca

2. It is an inert gas that does not react with metals or nonmetals.

B

3. It contains 1 more proton than an alkaline earth metal.

Ar

4. It is a metal that reacts vigorously with water

O

5. It has electrons located in 4 energy levels.




2.(JUNE 2000 416): Which of the following statements is completely TRUE?

  1. Na is an alkali metal and one from Ar's family is chemically active.
  2. Na is an alkali metal and fluorine is a metal.
  3. Be is an alkaline earth metal and Si is a metalloid.
  4. F is a halogen and can combine chemically with Ar.



3.(JUNE 1999 416): Four elements from the periodic table are described below.

Element

Characteristic

1

From period 2, it has 2 more electrons than helium.

2

A soft metal from period 3, it has one valence electron and reacts vigorously with water.

3

From period 4, it is found in bones and teeth.

4

From period 3, it has some of the properties of metals and nonmetals.
  1. 1 and 2
  2. 1 and 3
  3. 2 and 4
  4. 3 and 4

4.(JUNE 1998 416) The following table gives some information about four elemnts (E1, E2, E3 and E4).

 

# of protons

# of neutrons

# of electrons

Mass number

E1

19

20

 

 

E2

 

 

18

40

E3

 

12

 

24

E4

 

10

9

 

Which of these elements is an alkaline earth metal?

  1. E1
  2. E2
  3. E3
  4. E4

 

5. (JUNE 1998 416) Identify each of the following elements from the periodic table. Consider only the first 20 elements.

  1. The lightest element.
  2. A gas necessary for respiration.
  3. A halogen whose electrons are distributed among 3 energy levels.
  4. An element form period 2 that has 3 electrons in its outermost energy level.
  5. An inert gas used to fill balloons.
  6. A metal necessary for the formation of bones and teeth. ( in ionic form, of course)

 

Notes:

Family

Members

Valence Number = number of electrons found in last shell or energy level.( need not be memorized: just count number of horizontal blocks in periodic table from left to right, until you get to that element.)

Common ion formed when reacting

Physical properties

Chemical properties

 Alkali metals

 Li, Na, K, Rb, Cs, Fr

 1

+1

 Soft, low melting, shiny metals: conduct heat and electricity

 React vigorously with acids, water, oxygen and halogens.

 Alkaline earth metals

 Be, Mg, Ca, Sr, Ba, Ra

 2

+2

 Harder, higher-melting metals: conduct heat and electricity

 React with acids, water, oxygen and halogens, but not always as violently as alkali metals.

 Halogens

 F, Cl, Br, I, At

 7

-1

 Some are gases (Cl2 and F2), liquid (Br2) and solids(I2, At2) at room temp. Poor conductors.

 React with most metals, and form diatomic molecules.

 Noble or "Inert gases"

 He, Ne, Ar, Kr, Xe, Rn

 8

0

 All gase at room temperature. Poor conductors.

 Generally, not chemically active. Will only interact with powerful electron muggers.

Why is the common ion for alkali metals +1 but -1 for halogens? Each of the above families strives to get a noble gas shell diagram. Alkali metals all have one valence electron, one more than what the nearest noble gas has. So they like to lose it and form a +1 ion. Remember electrons have a negative charge. So by losing 1 electron, they end up with one more proton (positive charge) than electrons:

Charge = # of protons - # of electrons

Each halogen has 7 valence electrons, 1 less than the neighbouring noble gas. So they like to gain an electron to imitate the stable noble gas shell diagram.

For this reason, noble gases are relatively inert, but halogens, alkali metals and alkaline earth metals are all very reactive. In nature are not found in their neutral state: they have already reacted! Instead we find them in compound form: as ions bounded to other ions.

Example:

Neutral fluorine (F2) is extremely reactive: it is also one the most poisonous of the elements. But fluoride (F-1), at least in small amounts, is far less dangerous. In fact, it’s added to toothpaste.