STRUCTURE OF AN ATOM

What are atoms and molecules considered to be?

Fundamental building blocks of matter.

What was one major challenge for scientists at the end of the 19th century?

To reveal the structure of the atom and explain its properties.

Who discovered the electron?

J.J. Thomson.

What did E. Goldstein discover in 1886?

Canal rays, which are positively charged radiations.

What are the charges of protons and electrons?

Protons have a charge of +1, electrons have a charge of -1.

What was Thomson's model of the atom compared to?

A Christmas pudding or a watermelon.

According to Rutherford’s experiment, what does the nucleus contain?

Protons and nearly all the mass of the atom.

What are the drawbacks of Rutherford's model of the atom?

It could not explain the stability of the atom as revolving electrons would radiate energy and fall into the nucleus.

What is the main postulate of Bohr's model of the atom?

Electrons exist in discrete orbits and do not radiate energy while in these orbits.

What did J. Chadwick discover in 1932?

Neutrons, which are neutral particles present in the nucleus.

Define the term 'valency' in the context of atoms.

Valency is the combining capacity of an atom based on the number of electrons in its outermost shell.

What does the atomic number represent?

The number of protons in the nucleus of an atom.

What is an isotope?

Atoms of the same element with the same atomic number but different mass numbers.

Give an example of isobars.

Calcium and Argon both with mass number 40, but different atomic numbers.

How is the mass number calculated?

The sum of the total number of protons and neutrons present in the nucleus of an atom.

What was the outcome of Rutherford's alpha-particle scattering experiment?

It revealed that most of the atom is empty space and that positive charge and mass are concentrated in a small nucleus.

Explain the term 'canal rays'.

Positively charged radiations discovered by E. Goldstein.

What indicates that an atom is neutral according to Thomson's model?

The equal magnitude of positive and negative charges within the atom.

List the three sub-atomic particles of an atom.

Electrons, protons, and neutrons.

How are electrons distributed in an atom according to Bohr?

In shells or energy levels with specific capacities.

What does the term 'nucleons' refer to?

Protons and neutrons present in the nucleus of an atom.