Science Grade 8 Quiz

Who developed the first scientific atomic theory?

• Bohr

• Thomson

• Dalton

• Rutherford

Answer explanation

John Dalton developed the first scientific atomic theory in the early 19th century, proposing that matter is made up of indivisible atoms, each with a specific weight. This laid the foundation for modern chemistry.

Which particle has a negative charge?

• Proton

• Neutron

• Electron

• Atom

Answer explanation

The electron is the particle that carries a negative charge, while protons have a positive charge and neutrons are neutral. Atoms are made up of these particles, but they do not have a charge themselves.

Where are protons and neutrons located in an atom?

• In the electron cloud

• In the nucleus

• In the outer shell

• Floating freely

Answer explanation

Protons and neutrons are located in the nucleus of an atom, which is the central part. The electron cloud surrounds the nucleus, while the outer shell refers to the arrangement of electrons, not protons and neutrons.

What experiment led Rutherford to discover the nucleus?

• Flame test

• Gold foil experiment

• Water displacement

• Cloud chamber

Answer explanation

Rutherford's gold foil experiment involved firing alpha particles at a thin gold sheet. Most passed through, but some were deflected, leading him to conclude that an atom has a small, dense nucleus, thus discovering the nucleus.

Which scientist proposed that electrons orbit in fixed energy levels?

• Schrödinger

• Rutherford

• Bohr

• Dalton

Answer explanation

Niels Bohr proposed that electrons orbit the nucleus in fixed energy levels, known as orbits, which was a key development in atomic theory. This model helped explain the quantized nature of electron energies.

What is the charge of a neutron?

• +1

• −1

• 0

• Depends on the atom

Answer explanation

A neutron has no electric charge, which is why its charge is represented as 0. Unlike protons and electrons, which have positive and negative charges respectively, neutrons are neutral particles.

What is a pure element?

• A mixture of atoms

• One type of atom

• An alloy

• A compound

Answer explanation

A pure element consists of only one type of atom, making it distinct from mixtures, alloys, or compounds, which contain multiple types of atoms or elements.

What does a compound always have?

• Fixed ratio of elements

• Variable properties

• Easily separated parts

• Physical mixture

Answer explanation

A compound always has a fixed ratio of elements, meaning the elements combine in specific proportions. This distinguishes compounds from mixtures, which can have variable properties and easily separable parts.

Which is NOT a property of a mixture?

• Chemically bonded

• Keeps original properties

• Easy to separate

• Variable proportions

Answer explanation

A mixture consists of two or more substances that are not chemically bonded, allowing them to retain their original properties. Therefore, 'Chemically bonded' is NOT a property of a mixture.

What does the karat system measure?

• Weight of silver

• Size of crystals

• Purity of gold

• Heat conductivity

Answer explanation

The karat system measures the purity of gold, indicating how much of the metal is pure gold compared to other metals. A higher karat number means a higher gold content.