1.2 Atomic Structure & The Periodic Table (WJEC GCSE Chemistry): Flashcards

The number of neutrons equals the mass number minus the atomic number.

Beryllium has 4 protons, 4 electrons, and 5 neutrons (9 - 4 = 5).

Isotopes are atoms of the same element that have the same number of protons but a different number of neutrons.

False.

Isotopes have the same number of outer electrons, so they have identical chemical properties. They differ only in the number of neutrons, which adds mass but does not affect chemistry.

Both have 6 protons and 6 electrons. They differ in the number of neutrons: C-12 has 6 neutrons and C-14 has 8 neutrons.

False.

The atomic number is the number of protons, which never changes in a chemical reaction. Electrons can be lost, gained, or shared, but the number of protons stays the same.

Relative atomic mass is the weighted average mass of the isotopes of an element compared to 1/12th the mass of a carbon-12 atom. It has no units.

Relative atomic mass has no units because it is a ratio. It compares the average mass of an atom of the element to 1/12th the mass of a carbon-12 atom.

To calculate relative atomic mass, you multiply the percentage abundance of each isotope by its mass number, add the results together, then divide by 100.

The relative atomic mass is 85.6.

((72 × 85) + (28 × 87)) ÷ 100 = (6120 + 2436) ÷ 100 = 8556 ÷ 100 = 85.6

False.

Relative atomic mass is a weighted average of all the isotopes of an element. Because isotopes exist in different proportions, the result is often a decimal number (e.g. chlorine is approximately 35.5).

Different isotopes have the same atomic number because they have the same number of protons. They have different mass numbers because they have different numbers of neutrons.

True.

The relative atomic mass scale uses 1/12th the mass of a carbon-12 atom as its reference unit. All other elements are measured by comparison to this value.

Elements are arranged in order of increasing atomic number. This places elements with similar properties into the same vertical column (group).

A group is a vertical column in the Periodic Table. Elements in the same group have the same number of electrons in their outer shell and show similar chemical properties.

A period is a horizontal row in the Periodic Table. The period number indicates how many occupied electron shells the atoms of that element have.

Metals are found on the left and centre of the Periodic Table, while non-metals are found on the right side.

False.

Metallic character decreases across a period from left to right. Atoms on the right of the periodic table more readily accept electrons to fill their valence shells, so they behave as non-metals.

The group number tells you how many electrons are in the outermost (valence) shell of the element's atoms. For example, Group 6 elements have 6 outer electrons.

A metalloid is an element that displays properties of both metals and non-metals. Metalloids are found along the boundary between metals and non-metals in the Periodic Table.

False.

Elements in the same group (not period) share similar chemical properties, because they have the same number of outer electrons. Elements in the same period have the same number of electron shells but very different properties.

The first shell holds up to 2 electrons, the second shell holds up to 8 electrons, and the third shell holds up to 8 electrons (in the simplified model used at GCSE).

The electronic configuration of sodium is 2,8,1, and of chlorine is 2,8,7.

An electronic configuration is a notation showing the number of electrons in each shell of an atom, written as numbers separated by commas (e.g. 2,8,1 for sodium).

It is in Group 6, Period 3. The last number (6) gives the group, and the number of shells (3) gives the period.

True.

Electrons always fill the lowest available energy level first. The first shell (closest to the nucleus) fills before the second, and so on.

Na⁺ has the electronic configuration 2,8. A neutral sodium atom is 2,8,1. The ion has lost one electron from the outer shell to form a stable full outer shell.

The period an element belongs to is determined by the number of occupied electron shells, and the group is determined by the number of outer electrons.

False.

Elements in the same group have the same number of outer electrons, not the same number of shells. Elements in the same period share the same number of occupied shells.

Group 1 ions have a 1+ charge. They form when a Group 1 atom loses the single electron in its outer shell, giving it the electronic configuration of a noble gas.

Group 7 ions have a 1- charge. They form when a Group 7 atom gains one electron to complete its outer shell of 8 electrons.

False.

Melting points of Group 1 metals decrease going down the group, because the attractive forces between outer electrons and the positive nucleus get weaker as more electron shells are added.

Going down Group 7, chlorine is a pale yellow-green gas, bromine is a red-brown liquid, and iodine is a grey-black solid.

Reactivity increases going down Group 1 because more electron shells are added, placing the outer electron further from the nucleus. The weaker attraction means the outer electron is lost more easily.

Reactivity decreases going down Group 7 because more electron shells are added, so the electron being gained is further from the nucleus. The weaker attraction makes it harder for the atom to gain an electron.

True.

Melting and boiling points increase going down Group 7 because the atoms become larger, leading to stronger intermolecular forces that require more energy to overcome.

Group 1 metals are soft, have low densities, and have low melting points compared to most other metals. Their reactivity increases going down the group.

When an alkali metal reacts with water, a metal hydroxide and hydrogen gas are produced.

Sodium reacts with water to form sodium hydroxide and hydrogen. The solution formed has a pH greater than 7.

True.

Alkali metals react readily with both oxygen and water vapour in air, so they are stored in oil to keep them from tarnishing or reacting dangerously.

The word equation for potassium reacting with oxygen is:\n\n{align=center} potassium + oxygen → potassium oxide

A metal halide is an ionic salt formed when a Group 1 metal reacts with a halogen (Group 7 element). For example, sodium reacting with chlorine forms sodium chloride.

The reactions become more vigorous going down Group 1. Lithium reacts relatively slowly, sodium reacts more vigorously, and potassium reacts even more vigorously, burning with a lilac flame.

When potassium reacts with a halogen, the product is a white solid. The symbol equation for potassium reacting with chlorine is 2K (s) + Cl₂ (g) → 2KCl (s).

False.

All Group 1 metals produce alkaline solutions (pH greater than 7) when they react with water. This is why they are called alkali metals.

Hold a lit splint at the open end of a test tube containing the gas. A positive result is a loud squeaky pop.

The squeaky pop test is a method to identify hydrogen gas. A lit splint is held at the mouth of a test tube of gas. Hydrogen burns rapidly with oxygen to produce a loud squeaky pop sound and water.

False.

The lit splint should be held at the open mouth of the test tube, not inserted inside it. The gas needs oxygen at the opening to burn and produce the squeaky pop.

When hydrogen burns, it reacts with oxygen to produce water. This rapid combustion is what causes the squeaky pop sound in the hydrogen test.

To test for hydrogen, a lit splint is held at the mouth of a test tube. A positive result is a loud squeaky pop.

The hydrogen test uses a lit splint, which produces a squeaky pop. The oxygen test uses a glowing splint, which relights in the presence of oxygen.

False.

It is oxygen that relights a glowing splint. Hydrogen burns with a squeaky pop when a lit splint is held at the mouth of the test tube.

An ionic metal halide salt is formed. For example, sodium reacts with chlorine to form sodium chloride (NaCl).

Chlorine reacts with potassium bromide solution in a displacement reaction. The solution turns orange as bromine is displaced. The equation is Cl₂ + 2KBr → 2KCl + Br₂.

False.

A halogen can only displace a less reactive halogen from solution. Iodine is less reactive than chlorine, so iodine cannot displace chlorine. Chlorine can displace iodine.

Chlorine is used to sterilise drinking water and kill bacteria in swimming pools. Iodine is used as an antiseptic in plasters and sterilising sprays.

A halogen displacement reaction is a reaction in which a more reactive halogen displaces a less reactive halogen from an aqueous solution of its metal halide. The reactivity decreases going down Group 7.

Chlorine is a pale yellow-green gas at room temperature. Iodine is a dark grey solid that forms a purple vapour when warmed.

True.

Halogens do react with iron to form iron halides. The reaction becomes less vigorous going down Group 7, as reactivity decreases from fluorine to iodine.

Both chlorine and iodine exist as diatomic molecules. Although both are in Group 7, chlorine is a gas and iodine is a solid at room temperature.

Group 0 elements are unreactive because they have full outer electron shells, which is an extremely stable electronic configuration, so they have no tendency to gain or lose electrons.

A noble gas is an element from Group 0 of the Periodic Table. Noble gases are monoatomic, colourless, and chemically inert because their outer electron shells are completely full.

Helium is used in airships and weather balloons because it has a very low density and is unreactive.

False.

Most noble gases have 8 outer electrons, but helium is an exception with only 2 electrons, which still fills its first and only shell completely.

Neon is used in advertising signs because it emits light when an electric current passes through it.

Argon is used in light bulbs and as an inert atmosphere for welding because it is unreactive and will not react with hot metal filaments or welds.

Group 0 gases are all colourless gases at room temperature and are described as monoatomic, meaning each molecule consists of a single atom.

True.

Noble gases are all gaseous at room temperature and have very low melting and boiling points, consistent with their simple monoatomic structure and weak intermolecular forces.

The flame test is used to identify metal cations (positive ions) in a sample by the colour of the flame they produce when heated in a Bunsen burner flame.

Silver nitrate solution is added. A positive result is a coloured precipitate: white for chloride, cream for bromide, and yellow for iodide.

True.

The wire must be cleaned in dilute acid and heated until no colour appears in the flame. This prevents contamination from other ions, which could mask the colour produced by the sample being tested.

A precipitate is an insoluble solid that forms when two solutions are mixed and a chemical reaction occurs. For example, adding silver nitrate to a halide solution forms a coloured silver halide precipitate.

Ag⁺ (aq) + Cl^- (aq) → AgCl (s)\n\nA white precipitate of silver chloride is formed.

False.

Silver iodide forms a yellow precipitate. Silver chloride forms a white precipitate and silver bromide forms a cream precipitate.

Halide ions are the anions formed by Group 7 elements. They are identified using silver nitrate solution, which forms a precipitate if a halide ion is present.

The three tests are:\n\n1. A flame test (to identify the metal cation)\n2. A carbonate test using dilute hydrochloric acid and limewater (to test for carbonate ions)\n3. A silver nitrate test (to identify halide anions)

To test for carbonate ions, add dilute hydrochloric acid to the sample, then bubble any gas produced through limewater. A positive result is that the limewater turns cloudy.

The ionic compound is potassium bromide. A lilac flame indicates K⁺ ions, and a cream precipitate with silver nitrate indicates Br^- ions.

True.

If too much acid is added, the reaction can bubble over and carry acid into the limewater. The acid would dissolve any cloudy precipitate, giving a false negative result.

The ionic compound is calcium carbonate. A brick-red flame indicates Ca²⁺ ions, and fizzing that turns limewater cloudy indicates carbonate (CO₃^2-) ions.

In the flame test, sodium (Na⁺) gives a yellow-orange flame, barium (Ba²⁺) gives an apple-green flame, and lithium (Li⁺) gives a red flame.

False.

A yellow precipitate indicates iodide ions (AgI). Chloride ions give a white precipitate (AgCl), and bromide ions give a cream precipitate (AgBr).

Each test identifies only one type of ion. The flame test identifies the metal cation, the carbonate test identifies carbonate anions, and the silver nitrate test identifies halide anions. All three are needed to fully identify the compound.