Question

Question 9 Which of the following statements is false for an element having the electron configuration as 1s22s22p635" ? It is an element of the third period. It has only one valence electron. It is an alkali metal. It has a high electronegativity.

Answer 1

Answer:

The false statement for an element having the electron configuration as 1s², 2s², 2p⁶, 3s¹ is it has a high electronegativity.

Explanation: The element having the electron configuration 1s², 2s², 2p⁶, 3s¹ has number of electrons = 11.

Hence the number of protons present in element = number of electrons = 11.

Hence the atomic number of element = 11.

Hence the element is sodium (Na) with atomic number 11.

Option 1: It is an element of the third period. - True.

Explanation: The horizontal rows in the periodic table are called as periods. There are seven periods in the periodic table. In the periodic table from top to bottom that is from first period to seventh period, a new period begins when a new principal energy level begins filling with electrons.

Therefore in first period elements the last electron is present in K principle shell. (1s)

The second period starts when L principal energy level begins filling with electrons. Here in second period elements the last electron is present in 2s or 2p orbital.

The third period starts when M principal energy level begins filling with electrons. Here in third period elements the last electron is present in 3s or 3p orbital.

The electron configuration of given element is 1s², 2s², 2p⁶, 3s¹. Here last electron is present in M principle shell (3s orbital). Therefore given element is an element of the third period.

Option 2 :

It has only one valence electron:True

Explanation: The electron configuration of given element is 1s², 2s², 2p⁶, 3s¹. Hence the given element has a full innermost electron shell (K) of two electrons and a full shell (M) of eight electrons. The third shell, which is the outermost and the valence shell, has only one electron. Hence the given element can donate one electron eaisily in order to have a full outer energy level, because this will give it the most stable arrangement of electrons, the electronic configutration of noble gas Neon. Hence as sodium can donate one electron it has one valency.

Option 3: It is an alkali metal: True

Explanation:

The alkali metals are the metals which upon reaction with water forms alkalies. Henec the given element is sodium which can reacts with water and form sodium hydroxide as alkali.

Na(s) + H₂O   $\rightarrow$ NaOH(aq) + H₂(g) . Hence the given element is alkali metal as it reacts with water and forms alkali. Also in periodic table the elements present in IA group are alkali metals. Here sodium is present in IA group, hence it is alkali metal.

Option 4: It has a high electronegativity: False

Explanation:

Electronegativity: It is the tendency of an atom to attract a shared pair of electrons (or electron density) towards itself.

Electropositivity:  It is the tendency of an atom to lose electrons and form positive ions in chemical react

The electron configuration of given element, sodium is 1s², 2s², 2p⁶, 3s¹. Hence sodium can donate valence electron easily and acquire stable electronic configuration of neon. Hence given element is electropositive as it has tendencey to lose valence electron.