Page 191 - Chemistry ICSE Class X
P. 191
Metallurgy 177
Extraction. Alkaline earth metals are obtained by electrolytic reduction
method using molten halides.
Flame colour. Calcium, strontium, barium and radium and their
JCNKFGU KORCTV EJCTCEVGTKUVKE EQNQWTU VQ C PQPNWOKPQWU ƀCOG
Element: Calcium Strontium Barium Radium
Flame colour: Black-red Crimson Apple green Red
Action of air. All alkaline earth metals form oxides of the formula MO
(M = Mg, Ca, Ba, Sr).
burn
2Mg(s) + O (g) o 2MgO(s)
2
magnesium oxygen magnesium oxide
(white powder)
Magnesium burns in air with dazzling light.
2Ca(s) + O (g) o 2CaO(s)
2
calcium calcium oxide (lime)
The oxides of alkaline earth metals are basic in character. When
dissolved in water, these oxides give the corresponding alkalis.
Action of water. All alkaline earth metals, except beryllium,
decompose water giving hydrogen gas. Magnesium decompose only
boiling water.
boiling
Mg(s) + 2H O(l) o Mg(OH) (aq) + H (g)
2
2
2
room
Ca(s) + 2H O(l) o Ca(OH) (aq) + H (g)
2
2
2
temp.
The reactivity towards water increases down the group.
Action of acids. Alkaline earth metals react with dilute acids forming
the corresponding salt and liberating hydrogen gas. For example,
Mg(s) + 2HCl(aq) o MgCl (aq) + H (g)
2
2
dil. hydrochloric magnesium hydrogen
acid chloride
Illustrative Questions
23
19
Q.1. Which of the following elements, X and Y, is a metal?
9
11
Ans. $CUGF QP VJG CVQOKE PWODGT VJG GNGEVTQPKE EQPſIWTCVKQP QH VJG VYQ GNGOGPVU : CPF ; CTG
Element Atomic number K L M
23 X 11 2, 8, 1
11
19 Y 9 2, 7
9
Metals usually have 1 to 3 electrons in their outermost shell (all inner shells are complete). Therefore, element X
is a metal.
Q.2. 6JG GNGEVTQPKE EQPſIWTCVKQPU QH VYQ GNGOGPVU # CPF $ CTG CPF TGURGEVKXGN[ 9JKEJ QPG QH VJGO KU C
metal and which is a nonmetal?
Ans. The element A has only one electron in its outermost shell (all inner shells being complete). Therefore, element
A is a metal.
The element B has seven electrons in its outermost shell (all inner shells being complete).
Therefore, element B is a nonmetal.
