Atoms Structure - Class 7 Chemistry ICSE Free MCQ Test with solutions

Copper is an example of an element with variable valency, as it can exhibit different valencies, such as +1 or +2. This property is important in many chemical reactions and affects how copper compounds behave in different contexts.

A diatomic molecule consists of two atoms of the same element bonded together, such as O₂ (oxygen) or H₂ (hydrogen). These molecules are essential for life and are commonly found in nature as gases.

Monovalent elements have a valency of 1, meaning they can form one bond with another atom. Examples include hydrogen and sodium. Understanding valency is essential for predicting how elements will interact in chemical reactions.

Atomicity refers to the number of atoms that make up a molecule of an element. It helps classify molecules as monoatomic, diatomic, triatomic, or polyatomic based on their composition. For example, O₂ is diatomic and consists of two oxygen atoms.

A chemical formula serves to indicate the number of atoms of each element present in a molecule of a compound. This information is vital for understanding the composition and stoichiometry of chemical reactions.

There are 118 known elements in the periodic table. Each element is arranged by increasing atomic number, and they are grouped according to similar properties, which aids in the study of chemistry.

An atom is the fundamental unit of matter and is the smallest particle that retains the properties of an element. Unlike molecules, which are formed when two or more atoms bond together, atoms cannot exist alone in their elemental form.

The mass number (A) is the total count of protons and neutrons in an atom's nucleus. It is crucial for understanding isotopes of elements, which have the same number of protons but different mass numbers due to varying neutron counts.

When an atom loses an electron, it becomes a cation, acquiring a positive charge. This process is fundamental in the formation of ionic compounds, where cations and anions attract each other to form stable structures.

Electrons are subatomic particles with a negative charge. They orbit the nucleus of an atom, which contains positively charged protons and neutrally charged neutrons. Understanding the charge of these particles is crucial in the study of chemistry and electricity.

The atomic number is defined as the number of protons in the nucleus of an atom. It uniquely identifies an element and determines its position in the periodic table. For example, hydrogen has an atomic number of 1, indicating it has one proton.

Valency refers to the capacity of an atom to form bonds by either donating or accepting electrons. It is a crucial concept in understanding chemical reactions and bonding, as it helps in writing correct chemical formulas.

O₃ is the chemical formula for ozone, a triatomic molecule consisting of three oxygen atoms. Ozone plays a critical role in absorbing harmful ultraviolet radiation from the sun in the Earth's atmosphere.

Molecules of compounds are formed when atoms of different elements combine in fixed proportions, whereas molecules of elements consist of atoms of the same type. This distinction is fundamental to understanding the diversity of chemical substances.

Dmitri Mendeleev is renowned for creating the periodic table and formulating the Periodic Law, which organizes elements based on their atomic number and properties. His work laid the foundation for modern chemistry and helped predict the existence of undiscovered elements.