krit.club logo

Chemical Substances - The Periodic Table

Grade 6Cambridge (IGCSE)

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

•

An element is a pure substance made of only one type of atom. Each element is represented by a unique chemical symbol, such as HH for Hydrogen or OO for Oxygen.

•

The Periodic Table is an arrangement of elements in order of increasing atomic number (ZZ).

•

Groups are the vertical columns in the Periodic Table. Elements in the same group have similar chemical properties (e.g., Group 1 elements are the reactive Alkali Metals).

•

Periods are the horizontal rows. Elements in the same period have the same number of electron shells.

•

Metals are located on the left and center of the Periodic Table, while non-metals are found on the right (separated by a zig-zag line of metalloids).

•

The Atomic Number (ZZ) represents the number of protons in the nucleus of an atom. In a neutral atom, the number of electrons also equals ZZ.

•

The Mass Number (AA) represents the total number of protons and neutrons in the nucleus.

•

Molecules are formed when two or more atoms are chemically bonded together. For example, a molecule of Oxygen gas is represented as O2O_2.

📐Formulae

A=Z+nA = Z + n

n=A−Zn = A - Z

Number of Electrons=Number of Protons (for neutral atoms)\text{Number of Electrons} = \text{Number of Protons (for neutral atoms)}

💡Examples

Problem 1:

An atom of Carbon is represented by the symbol 612C^{12}_{6}C. Calculate the number of protons, neutrons, and electrons present in this neutral atom.

Solution:

Protons = 66, Electrons = 66, Neutrons = 66.

Explanation:

The atomic number (ZZ) is the bottom number, so there are 66 protons. Since it is neutral, there are 66 electrons. The mass number (AA) is 1212. Using the formula n=A−Zn = A - Z, we get 12−6=612 - 6 = 6 neutrons.

Problem 2:

Determine the total number of atoms in a single molecule of Sulfuric Acid, which has the chemical formula H2SO4H_2SO_4.

Solution:

77 atoms.

Explanation:

The formula H2SO4H_2SO_4 consists of 22 atoms of Hydrogen (HH), 11 atom of Sulfur (SS), and 44 atoms of Oxygen (OO). Summing them up: 2+1+4=72 + 1 + 4 = 7.

Problem 3:

Identify the element in Period 2, Group 18 (Group 0) of the Periodic Table.

Solution:

NeNe (Neon).

Explanation:

Period 2 indicates the second row. Group 18 (or Group 0) contains the Noble Gases. The element at the intersection of the second row and the last column is Neon, symbol NeNe.