Atomic Structure Flashcards

All 18 cards in this deck

What did Dalton's model say about whether an atom can be divided?

Atoms are indivisible — not formed of any smaller particles.

Give two differences between Dalton's model of atoms and today's model.

Modern atoms are formed of sub-atomic particles (protons, neutrons, electrons) and have a nucleus.

True or false? In today's model, atoms of the same element can have different numbers of neutrons.

True. Isotopes exist — Dalton had said all atoms of an element are identical.

Describe the structure of an atom.

A nucleus containing protons and neutrons, surrounded by electrons in shells.

What are the relative charge and relative mass of a proton?

Relative charge $+1$, relative mass $1$.

What are the relative charge and relative mass of a neutron?

Relative charge $0$, relative mass $1$.

What are the relative charge and relative mass of an electron?

Relative charge $-1$, relative mass $\frac{1}{1836}$ (very small).

Why does an atom have no overall charge?

It has the same number of protons and electrons, so the $+1$ and $-1$ charges cancel out.

How does the size of the nucleus compare with the size of the whole atom?

The nucleus is very small compared with the overall size of the atom.

Where is most of the mass of an atom found?

Concentrated in the nucleus.

What is meant by the mass number of an atom?

The total number of protons and neutrons in the atom.

What is meant by the atomic number of an atom?

The number of protons in the nucleus — the same for every atom of an element and unique to that element.

What are isotopes?

Atoms of the same element with the same number of protons but different numbers of neutrons.

True or false? Isotopes of an element have different numbers of electrons.

False. They have the same number of protons and electrons; only the number of neutrons differs.

How do you find the number of neutrons in an atom from its atomic number and mass number?

number of neutrons = mass number − atomic number (the number of protons and the number of electrons both equal the atomic number)

What does a relative atomic mass that is not a whole number tell you about an element's atoms?

The element exists as a mixture of isotopes, with different numbers of neutrons and so different mass numbers.
e.g. chlorine, 35.5, is a mixture of chlorine-35 and chlorine-37.

What was the plum pudding model of the atom?

The model proposed after electrons were discovered: an atom is a ball of positive charge with negative electrons dotted through it.

Why was the plum pudding model replaced by the nuclear model of the atom?

Experiments showed that the positive charge is not spread through the atom: it is concentrated in a tiny nucleus at the centre, which also holds most of the mass.