atomic structure and periodic table

Question 1

What is the structure of an atom?

Answer 1

An atom consists of a nucleus containing protons and neutrons, surrounded by electrons in shells (energy levels).

Question 2

Define “atomic number” and “mass number.”

Answer 2

Atomic number: The number of protons in an atom. It determines the element.
Mass number: The sum of protons and neutrons in the nucleus.

Question 3

What is an isotope?

Answer 3

Isotopes are atoms of the same element (same number of protons) but with different numbers of neutrons

Question 4

Why do isotopes of an element have the same chemical properties?

Answer 4

Chemical properties depend on the number of electrons and their arrangement, which are the same in isotopes.

Question 5

Explain how to calculate the relative atomic mass (Ar) of an element from its isotopes.

Answer 5

Relativeatomicmass(Ar)=
sum of (isotope mass x abundance) / total abundance

Question 6

Chlorine has isotopes Cl-35 (75%) and Cl-37 (25%):

Answer 6

( 38 x 75) + (37 x 25)
Ar = ——————————-
100
= 35.5

Question 7

How is the periodic table arranged?

Answer 7

Elements are arranged in order of increasing atomic number

Question 8

Why do elements in Group 1 (alkali metals) become more reactive as you go down the group?

Answer 8

As you go down Group 1:
The outer electron is farther from the nucleus.
Shielding by inner electrons increases.
This makes it easier to lose the outer electron, increasing reactivity.

Question 9

Why do noble gases (Group 0) not react easily?

Answer 9

Noble gases have a full outer shell of electrons, making them stable and unreactive.

Question 10

What happens when a metal reacts with a non-metal?

Answer 10

Metals lose electrons to form positive ions (cations), while non-metals gain electrons to form negative ions (anions). These oppositely charged ions attract, forming an ionic bond.

Question 11

Explain why magnesium has a higher melting point than sodium.

Answer 11

Magnesium has two outer electrons, which are delocalized in its metallic bonding. This creates a stronger attraction between the positive ions and the sea of electrons compared to sodium, which has only one outer electron.

Question 12

Why do transition metals have high melting points?

Answer 12

Transition metals have strong metallic bonds due to a high number of delocalized electrons. This makes their melting points higher than Group 1 metals