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Chemistry - The Periodic Table Introduction

Grade 7IGCSE

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

🔑Concepts

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The Periodic Table is a tabular display of all known chemical elements, organized by increasing Atomic Number (ZZ).

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Groups are the vertical columns in the table. Elements in the same group have the same number of valence electrons (electrons in the outer shell) and exhibit similar chemical properties.

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Periods are the horizontal rows. The period number corresponds to the number of electron shells (energy levels) an atom possesses.

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Metals are located on the left side of the staircase line, while non-metals are located on the right side. Metalloids (semi-metals) lie along the boundary.

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Group 1 elements are known as Alkali Metals, Group 7 as Halogens, and Group 0 (or 8) as Noble Gases. Noble gases are monatomic and chemically unreactive due to a full outer shell.

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Each element is represented by a symbol. For example, Hydrogen is HH, Helium is HeHe, and Sodium is NaNa.

📐Formulae

Atomic Number (Z)=Number of ProtonsAtomic\ Number\ (Z) = Number\ of\ Protons

Mass Number (A)=Number of Protons+Number of NeutronsMass\ Number\ (A) = Number\ of\ Protons + Number\ of\ Neutrons

Number of Neutrons=A−ZNumber\ of\ Neutrons = A - Z

Charge of an Atom=Protons−Electrons=0 (for neutral atoms)Charge\ of\ an\ Atom = Protons - Electrons = 0\ (for\ neutral\ atoms)

💡Examples

Problem 1:

An atom of Lithium is represented as 37Li^{7}_{3}Li. Calculate the number of protons, neutrons, and electrons in a neutral Lithium atom.

Solution:

Protons = 33, Electrons = 33, Neutrons = 44.

Explanation:

The atomic number (subscript) is 33, which equals the number of protons and electrons. The mass number (superscript) is 77. The number of neutrons is found by A−ZA - Z, which is 7−3=47 - 3 = 4.

Problem 2:

Identify the element that has an electronic configuration of 2,8,12, 8, 1 and state its Group and Period.

Solution:

Element: Sodium (NaNa). Group: 11. Period: 33.

Explanation:

The total number of electrons is 2+8+1=112 + 8 + 1 = 11, which corresponds to the atomic number of Sodium (NaNa). Since there is 11 electron in the outermost shell, it is in Group 11. Since there are 33 shells occupied, it is in Period 33.

Problem 3:

Explain why Neon (NeNe), with an atomic number of 1010, is placed in Group 0.

Solution:

Neon has a full outer shell electronic configuration of 2,82, 8.

Explanation:

The first shell holds a maximum of 22 electrons and the second shell holds 88. Because the outer shell is complete with 88 electrons, NeNe is stable and unreactive, placing it in the Noble Gases (Group 0).