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 for Hydrogen or for Oxygen.
The Periodic Table is an arrangement of elements in order of increasing atomic number ().
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 () represents the number of protons in the nucleus of an atom. In a neutral atom, the number of electrons also equals .
The Mass Number () 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 .
📐Formulae
💡Examples
Problem 1:
An atom of Carbon is represented by the symbol . Calculate the number of protons, neutrons, and electrons present in this neutral atom.
Solution:
Protons = , Electrons = , Neutrons = .
Explanation:
The atomic number () is the bottom number, so there are protons. Since it is neutral, there are electrons. The mass number () is . Using the formula , we get neutrons.
Problem 2:
Determine the total number of atoms in a single molecule of Sulfuric Acid, which has the chemical formula .
Solution:
atoms.
Explanation:
The formula consists of atoms of Hydrogen (), atom of Sulfur (), and atoms of Oxygen (). Summing them up: .
Problem 3:
Identify the element in Period 2, Group 18 (Group 0) of the Periodic Table.
Solution:
(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 .