Atomic Structure Flashcards

All 29 cards in this deck

What did Dalton's model say an atom was?

A tiny solid sphere that cannot be divided into smaller particles, with all atoms of an element identical.

Which subatomic particle was discovered first, showing that Dalton's 'indivisible atom' was wrong?

The electron.

Name two features of today's model of the atom that were missing from Dalton's model.

Atoms are made of subatomic particles (protons, neutrons, electrons) and have a nucleus.

True or false? Dalton's model included a positively charged nucleus.

False. Dalton's atoms were solid indivisible spheres; the nucleus came later, after subatomic particles were discovered.

True or false? In today's model, all atoms of the same element are identical.

False. Isotopes of an element have different numbers of neutrons, so Dalton's idea was changed.

Which subatomic particle was the last of the three to be discovered?

The neutron.

Describe the structure of an atom.

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

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

Charge $+1$, mass $1$.

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

Charge $0$, mass $1$.

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

Charge $-1$, mass very small (about $\frac{1}{1835}$).

Why does an atom have no overall electrical charge?

It contains equal numbers of protons and electrons, so the $+1$ and $-1$ charges cancel out.

True or false? An atom is neutral because it has equal numbers of protons and neutrons.

False. It is neutral because it has equal numbers of protons and electrons; neutrons have no charge.

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

The nucleus is very small compared with the atom — about 10 000 times smaller in diameter.

Where is most of the mass of an atom concentrated?

In the nucleus, because protons and neutrons each have a relative mass of 1 while electrons have almost no mass.

What is the approximate diameter of an atom?

About $1 \times 10^{-10}$ m (0.1 nm).

True or false? Most of the volume of an atom is empty space.

True. The tiny nucleus is surrounded by electron shells with mostly empty space between.

What is the overall charge of the nucleus of an atom?

Positive, because it contains protons ($+1$) and neutrons (0).

What is meant by the mass number of an atom?

The total number of protons and neutrons in its nucleus.

What is meant by the atomic number of an atom?

The number of protons in its nucleus.

What are isotopes?

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

Which number identifies an element, and why?

The atomic number (number of protons) — every atom of an element has the same number of protons and no other element has that number.

What are the steps to find the numbers of protons, neutrons and electrons in an atom from its nuclear symbol?
e.g. $^{23}_{11}\mathrm{Na}$

1. Protons = atomic number (bottom number): 11
2. Electrons = protons, as an atom is neutral: 11
3. Neutrons = mass number − atomic number: $23 - 11 = 12$

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

False. They have the same numbers of protons and electrons, but different numbers of neutrons.

What is the relative atomic mass of an element?

The mean mass of its atoms, taking account of the masses and abundances of all its isotopes.

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

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

What are the steps to calculate relative atomic mass from isotopic masses and percentage abundances?
e.g. 20% of mass 10 and 80% of mass 11

1. Multiply each isotope mass by its % abundance: $10 \times 20 = 200$, $11 \times 80 = 880$
2. Add the results: $200 + 880 = 1080$
3. Divide by 100: relative atomic mass $= 10.8$

What are the steps to find an unknown isotope abundance from the relative atomic mass?
e.g. isotopes of mass 63 and 65, relative atomic mass 63.5

1. Let $x$ = % of the lighter isotope, so $(100 - x)$ = % of the heavier one
2. Write the equation: $\frac{63x + 65(100 - x)}{100} = 63.5$
3. Solve for $x$: 75% of mass 63 and 25% of mass 65

True or false? Chlorine's relative atomic mass is 35.5 because each chlorine atom contains half a neutron.

False. It is the weighted mean of chlorine-35 and chlorine-37 atoms; individual atoms have whole-number mass numbers.

True or false? The mass number of a single atom can be a decimal number.

False. Mass number is a count of protons plus neutrons, so it is always a whole number; only relative atomic mass can be a decimal.