Simple Model of the Atom Flashcards

All 55 cards in this deck

What is an atom?

The smallest part of an element that can exist.

What is an element?

A substance made of only one type of atom — all its atoms have the same number of protons.

How is each element represented in a formula?

By its chemical symbol: one capital letter, sometimes with a second small letter.
e.g. magnesium is $Mg$

True or false? All the atoms of a particular element have the same number of protons.

True. Atoms of different elements have different numbers of protons.

True or false? A substance made of molecules containing two atoms of the same element, such as $O_2$, is a compound.

False. It is an element — a compound must contain atoms of two or more different elements.

What is a compound?

A substance containing two or more elements chemically combined in fixed proportions.

How can a compound be separated into its elements?

Only by chemical reactions.

True or false? A compound can be separated into its elements by a physical process such as filtration.

False. Physical processes only separate mixtures; compounds need chemical reactions.

What does a compound name ending in '-ate' tell you?
e.g. copper sulfate

It contains oxygen as well as the other elements named — copper, sulfur and oxygen.

What does a small subscript number in a formula tell you?
e.g. the 2 in $CO_2$

The number of atoms of the element it follows — 2 oxygen atoms per carbon atom.

What is a word equation?

An equation giving the names of the reactants on the left of the arrow and the names of the products on the right.

In a balanced symbol equation, what must be the same on both sides?

The number of atoms of each element.

What are the steps to balance a symbol equation?
e.g. $H_2 + O_2 \rightarrow H_2O$

1. Count the atoms of each element on both sides: 2 O on the left, 1 O on the right.
2. Put large numbers in front of formulae to even them up: $H_2 + O_2 \rightarrow 2H_2O$.
3. Recount and adjust: $2H_2 + O_2 \rightarrow 2H_2O$.

True or false? You can balance an equation by changing the small subscript numbers inside a formula.

False. Only the large numbers in front of formulae may be changed; subscripts would change the substance.

What do the state symbols $(s)$, $(l)$, $(g)$ and $(aq)$ mean?

Solid, liquid, gas and aqueous (dissolved in water).

What is a half equation? (HT)

An equation showing the electrons lost or gained by one species, e.g. at an electrode.

What is an ionic equation? (HT)

An equation showing only the ions and substances that actually take part in the reaction, with spectator ions left out.

What is a spectator ion? (HT)

An ion that is unchanged in the reaction and appears on both sides, so it is left out of the ionic equation.

What are the steps to write a half equation for a metal ion gaining electrons at the cathode? (HT)
e.g. $Cu^{2+}$ forming copper

1. Write the ion on the left: $Cu^{2+}$.
2. Add electrons on the left to cancel the charge: $Cu^{2+} + 2e^-$.
3. Write the neutral product on the right: $Cu^{2+} + 2e^- \rightarrow Cu$.

What are the steps to write an ionic equation? (HT)
e.g. $HCl + NaOH \rightarrow NaCl + H_2O$

1. Write all aqueous compounds as separate ions: $H^+ + Cl^- + Na^+ + OH^- \rightarrow Na^+ + Cl^- + H_2O$.
2. Cancel ions that appear unchanged on both sides: $Na^+$ and $Cl^-$.
3. Write what is left: $H^+ + OH^- \rightarrow H_2O$.

True or false? In the half equation $Na \rightarrow Na^+ + e^-$, the sodium atom has gained an electron. (HT)

False. It has lost one electron — electrons on the right means loss (oxidation).

What is a mixture?

Two or more elements or compounds that are not chemically combined together.

What does filtration separate?

An insoluble solid from a liquid — the solid stays in the filter paper as the liquid passes through.

What does crystallisation separate, and how?

A soluble solid from its solution, by evaporating the solvent so crystals form.

Which technique gives pure water from salt solution, and why does it work?

Simple distillation — the water evaporates, is condensed and collected, leaving the salt behind.

What does fractional distillation separate?

A mixture of two or more liquids with different boiling points.

What does chromatography separate?

Substances in a mixture that dissolve in the same solvent, e.g. the dyes in an ink.

What is the plum pudding model of the atom?

A ball of positive charge with negative electrons embedded in it.

What conclusions came from the alpha particle scattering experiment?

The mass of an atom is concentrated at the centre (the nucleus) and the nucleus is charged.

What change did Niels Bohr make to the nuclear model?

He suggested electrons orbit the nucleus at specific distances (in energy levels/shells).

What did the experimental work of James Chadwick show?

Evidence for the existence of neutrons within the nucleus.

Put the electron, proton and neutron in the order they were discovered, earliest first.

Electron, proton, neutron.

True or false? In the plum pudding model most of the atom is empty space.

False. The plum pudding atom is solid positive charge throughout; it is the nuclear model that is mostly empty space.

What are the relative charges of a proton, a neutron and an electron?

Proton $+1$, neutron $0$, electron $-1$.

What are the relative masses of a proton, a neutron and an electron?

Proton 1, neutron 1, electron very small (about $\frac{1}{2000}$).

Where in an atom are the protons, neutrons and electrons found?

Protons and neutrons in the nucleus; electrons in shells (energy levels) around the nucleus.

What is the atomic number of an element?

The number of protons in one atom of that element.

True or false? An atom has no overall electrical charge because it has equal numbers of protons and electrons.

True. The $+1$ charges and $-1$ charges cancel out.

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

1. Protons = atomic number = 11.
2. Electrons = protons = 11.
3. Neutrons = mass number − atomic number = $23 - 11 = 12$.

What is the radius of an atom?

About $0.1$ nm, which is $1 \times 10^{-10}$ m.

How does the radius of the nucleus compare with the radius of the atom?

The nucleus is less than $\frac{1}{10\,000}$ of the radius of the atom (about $1 \times 10^{-14}$ m).

What is the mass number of an atom?

The sum of the protons and neutrons in the atom.

What are isotopes?

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

True or false? Isotopes of the same element react chemically in the same way.

True. They have the same number of electrons and so the same electronic structure.

What are the steps to find the number of electrons in an ion?
e.g. $O^{2-}$, atomic number 8

1. Electrons in the atom = atomic number = 8.
2. A negative charge means electrons gained; a positive charge means electrons lost.
3. Adjust: $8 + 2 = 10$ electrons.

What is the relative atomic mass of an element?

An average value that takes account of the abundance of the isotopes of the element.

What are the steps to calculate relative atomic mass from percentage abundances?
e.g. chlorine: 75% of mass number 35, 25% of mass number 37

1. Multiply each mass number by its percentage abundance: $35 \times 75 = 2625$ and $37 \times 25 = 925$.
2. Add the results: $2625 + 925 = 3550$.
3. Divide by 100: $A_r = 35.5$.

True or false? Relative atomic masses are always whole numbers.

False. They are averages over the isotopes, so they are often not whole numbers.

Which number of each isotope is used in a relative atomic mass calculation — the mass number or the atomic number?

The mass number, multiplied by that isotope's percentage abundance.

Which shells do electrons in an atom occupy first?

The lowest available energy levels — the innermost available shells.

How many electrons fill the first, second and third shells of an atom?

2 in the first, 8 in the second, 8 in the third.

What are the steps to write the electronic structure of an atom?
e.g. sodium, atomic number 11

1. Number of electrons = atomic number = 11.
2. Fill the first shell with 2, then the second with up to 8: 2, 8 used.
3. Put the rest in the next shell: $2,8,1$.

In an electronic structure written as numbers, what does the last number tell you?
e.g. $2,8,1$

The number of electrons in the outer shell — 1 for this atom.

In what two ways can the electronic structure of an atom be represented?

By numbers separated by commas (e.g. $2,8,3$) or by a diagram of electrons in shells.

True or false? You use the mass number of an element to work out its electronic structure.

False. You use the atomic number, which equals the number of electrons in the atom.