Atomic Structure Flashcards

All 19 cards in this deck

What did Dalton's model say about whether atoms could be split?

Atoms are indivisible — not formed of any smaller particles.

True or false? Dalton said all atoms of the same element are identical, but today's model says atoms of the same element can have different numbers of neutrons.

True. Isotopes exist, so atoms of one element can differ in neutron number.

Describe the structure of an atom.

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

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

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

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

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

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

Relative charge $-1$, relative mass very small ($\frac{1}{1835}$, taken as almost zero).

Why does an atom contain equal numbers of protons and electrons?

So the $+1$ charges of the protons are cancelled by the $-1$ charges of the electrons, giving the atom no overall charge.

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 (the protons and neutrons).

What is meant by the mass number of an atom?

The total number of protons and neutrons in its nucleus.
e.g. an atom with 17 protons and 18 neutrons has mass number 35.

What is meant by the atomic number of an atom?

The number of protons in its nucleus — this number is the same for all atoms of an element and is unique to that element.

What are isotopes?

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

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

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

True or false? Isotopes of an element have the same atomic number but different mass numbers.

True. Same protons gives the same atomic number; different neutrons gives different mass numbers.

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

protons = atomic number; electrons = protons (the atom is neutral); neutrons = mass number − atomic number

What is the equation for the relative atomic mass of an element from the masses and percentage abundances of its isotopes?

relative atomic mass = sum of (isotope mass × percentage abundance) ÷ 100

What is the relative atomic mass of an element?

The mean mass of its atoms, taking into account the mass and percentage abundance of each of its isotopes.

Why are the relative atomic masses of some elements not whole numbers?

Because the element exists as a mixture of isotopes of different masses, and the relative atomic mass is the weighted average of them.

True or false? Because chlorine has a relative atomic mass of 35.5, a chlorine atom can have a mass number of 35.5.

False. Mass numbers are always whole numbers; 35.5 is the average over the isotopes present.