Alkaline Earth Metals

Reasons of Naming Alkaline Earth Metals

The oxides of the three metals (Ca, Sr and Ba) were known much earlier than the metals themselves and were called alkaline earths, since they were alkaline in character and occurred in nature as earths [lime (CaO), strontia (SrO), baryta (BaO)]. Therefore, when Ca, Sr and Ba were discovered , they were named alkaline earth metals.

Physical Properties of alkaline earth metals

1. Physical state
2. Melting and boiling points
3. Atomic volume, atomic and ionic radii
4. Ionization energy
5. Electropositive character
5. Electronegativity
7. Flame coloration
8. Conductivity
9. Density
10. Hardness
11. Oxidation state
12. Solubility of salts

Atomic radius example of alkaline earth metals

Be(113pm)
Mg(160pm)
Ca(197pm)
Sr(215pm)
Ba(217pm)

Ionization energy example of alkaline earth metals

Be- 900 kJ/mol
Mg- 728 kJ/mol
Ca -690 kJ/mol
Sr-550 kJ/mol
Ba-503 kJ/mol

Color of Ca in flame coloration

Brick red

Color of Sr in flame coloration

Crimson

Which elements don't give any color in flame coloration and why?

Be and Mg do not give any color to the flame as they have higher ionization potential comparatively others.

Chemical properties of alkaline earth metals

1. Reaction with air
2. Reaction with hydrogen
3. Reaction with water
4. Reaction with acids
5. Reaction with halogens
6. Formation of carbides

Use and application of Be

-never been used
-regarded as one of the most toxic elements for common use

Use and application of Mg

-essential for life
-activator of many enzymes
-neuromuscular functions
Compounds
-Magnesium hydroxide
-Magnesium oxide
-Universal antidote
-Magnesium trisilicate
-talc

Use and application of Ca

-functions of nervous system
-proper cardiac function
-blood clotting
-structural basis of skeleton
Official compounds
-Calcium carbonate
-Calcium chloride
-Calcium gluconate
-Calcium lactate

Use and application of Sr

-adjuvant
-no official compound available

Use and application of Ba

-Barium chloride => very toxic
-Barium ion => produces local irritation
-Barium sulphate => used to help diagnose certain disorders of the esophagus, stomach or intestines

Use and application of Ra

-highly radioactive
-Radiation from radium can destroy living cells
-Radium salts were used to arrest and cure malignant growths

Similarities between alkali metals and alkaline earth metals

1. s-block
2. electropositive
3. great chemical reactivity
4. do not occur in the free state in nature
5. react with water to form metal hydroxides and H2
6. hydroxides give strong bases with water
7. extracted by electrolytic method from their salts
8. silvery in untarnished conditions

Dissimilarities between alkali metals and alkaline earth metals

1. harder, heavier and have higher melting points than alkali metals
2. less basic
3. Ca, Sr, Ba reacts less vigorously with water
4. Carbonate and sulphates
5. Phosphates

explain physical state of alkaline earth metals

-greyish white lustre when cut
-malleable

explain melting and boiling points of alkaline earth metals

-do not show any regular trend
-higher than alkali metals

explain atomic volume, atomic and ionic radii of alkaline earth metals

Because of the addition of an extra shell of electrons to each element from Be to Ra, the atomic volume increases from Be to Ra. With the increases of atomic volume, the atomic and ionic radii (of M2+ ions) also increase from Be to Ra.
The atomic radii of these elements are however smaller than those of alkali metals in the same period. This is since the alkaline earth metals have higher nuclear charge which tends to draw the orbit electrons toward the nucleus.

Explain ionization energies of alkaline earth metals

The first and second ionization energies of these elements decrease with the increase of atomic radii from Be to Ba.

Explain electropositive characters of alkaline earth metals

Although the ionization energies of these elements are higher than those of alkali metals, yet these are sufficiently low to make these metals to lose readily their ns2 electrons to form M2+ ions:
These metals, therefore, show strong electropositive character which increases from Be to Ba. Since these metals have higher ionization energies than the alkali metals, these are not strongly electropositive as the alkali metals.

Explain electronegativities of alkaline earth metals

These are small and decrease from Be to Ba.

Explain flame coloration of alkaline earth metals

Ca- Brick red
Sr- Crimson
Ba- Apple green
Ra- Red
Be and Mg do not give any color to the flame as they have higher ionization potential comparatively others.

Explain conductivity of alkaline earth metals

Since two valence electrons are free to move throughout the metal structure, the alkaline earth metals are good conductors of heat and electricity.

Explain density of alkaline earth metals

These elements have higher density than those of the alkali metals in the same period. Density decreases slightly up to Ca after which it increases.

Explain hardness of alkaline earth metals

These elements are harder than alkali metals.

Explain oxidation state of alkaline earth metals

Alkaline earth metals show +2 oxidation state.

explain solubility of salts of alkaline earth metals

The salts of alkaline earth metals are less soluble than those of alkali metals.

Explain reaction with air of alkaline earth metals

▪The alkaline earth metals react readily on heating with the oxygen (O2) and the nitrogen (N2) of the air to form oxides, MO and nitrides, M3N2.
2M + O2 → 2MO
3M + N2 → M3N2
▪Be reacts less rapidly and requires high temperatures for the formation of BeO.
▪Ba forms peroxides, BaO2, because of its greater activity.
Ba + O2 BaO2

Rate of reactivity, Be < Mg < Ca < Sr < Ba

Explain reaction with hydrogen of alkaline earth metals

▪Mg, Ca, Sr and Ba form hydrides when heated with hydrogen (H2) :
M + H2 → MH2
▪These hydrides readily react with H2O to liberate H2:
MH2 + H2O → M(OH)2 + H2

BeH2 cannot be prepared by the direct combination of Be and H2. It is however, prepared by reducing BeCl2 by LiH and LiAlH4.

BeCl2 + 2LiH BeH2 + 2LiCl

Explain reaction with water of alkaline earth metals

▪Alkaline earth metals react readily with H2O to give hydroxide:
M + 2H2O → M(OH)2 + H2
▪Be does not react with H2O even at elevated temperature. Mg reacts only with steam.

Explain reaction with acids of alkaline earth metals

Alkaline earth metals react vigorously with acids to form corresponding salts:
M + 2HCl → MCl2 + H2

Explain reaction with halogens of alkaline earth metals

Alkaline earth metals react with halogens (X2) to form corresponding halides:
M + X2 → MX2

Explain formation of carbides of alkaline earth metals

When the elements from Mg to Ba or their oxides are heated with carbon, carbides (MC2) are obtained.
Ca + 2C CaC2

Which group do these elements belong to?

group 2

Color of Ba in flame coloration

Apple green

Color of Ra in flame coloration

Red

Oxidation state of alkaline earth metals

+2 oxidation state.

Rate of reactivity of alkaline earth metals

Be < Mg < Ca < Sr < Ba