QCM : Introduction to Atomic and Periodic Chemistry — 16 questions

Questions et réponses du QCM

1. Which statement correctly describes how reactivity changes in Group 1 metals as you move down the group?

They become less reactive because they lose electrons less easily
They become more reactive because they gain electrons more easily
They become less reactive because their outer shell becomes full
They become more reactive because they lose electrons more easily

They become more reactive because they lose electrons more easily

Explication

Group 1 metals become more reactive down the group, and the trend is linked to losing the outer electron more easily. The outer shell does not become full; that describes Group 0 elements.

2. What does the period number of an element tell you?

The number of possible ions the element can form
The number of outer-shell electrons
The number of occupied electron shells
The total number of protons and neutrons

The number of occupied electron shells

Explication

The period number matches the number of occupied electron shells. Outer-shell electrons are indicated by the group number, not the period number.

3. How should a symbol equation be balanced?

By changing the coefficients in front of the formulas
By removing atoms from the equation until both sides match
By adding extra products until the masses are equal
By changing the subscripts in the formulas

By changing the coefficients in front of the formulas

Explication

Balancing is done by changing coefficients only, so the number of each type of atom is the same on both sides. Subscripts must not be altered because they change the substances themselves.

4. How is the relative formula mass of Na2CO3 calculated?

23 + 12 + 3 × 16
2 × 23 + 12 + 3 × 16
23 + 12 + 16
2 × 23 + 12 + 16

2 × 23 + 12 + 3 × 16

Explication

Relative formula mass is found by adding the Ar values of all atoms in the formula, including any multipliers. For Na2CO3, that is 2 × 23 + 12 + 3 × 16 = 106.

5. What do the reactants in a chemical equation represent?

The substances written on the left side of the arrow that take part in the reaction
The substances formed on the right side of the arrow
The substances that do not change during the reaction
The atoms that are added to make the equation balanced

The substances written on the left side of the arrow that take part in the reaction

Explication

Reactants are the starting substances and are written on the left side of the arrow. Products are the substances formed and written on the right.

6. Why must the formula of an ionic compound be electrically neutral overall?

Because ionic compounds contain no charged particles at all
Because the ion with the larger charge determines the formula alone
Because the positive charge of the metal must be cancelled by the negative charge of the non-metal
Because electrons are shared equally in ionic bonding

Because the positive charge of the metal must be cancelled by the negative charge of the non-metal

Explication

Ionic compounds are written so the total positive charge equals the total negative charge. This is why ion counts are adjusted until the charges cancel completely.

7. Which statement best describes isotopes of the same element?

They have the same mass number but different atomic numbers
They have the same number of protons but different numbers of neutrons
They have the same number of electrons but different charges
They have the same number of neutrons but different numbers of protons

They have the same number of protons but different numbers of neutrons

Explication

Isotopes are atoms of the same element, so they must have the same atomic number and therefore the same number of protons. They differ in the number of neutrons, which changes the mass number.

8. Which noble gas is commonly used to fill balloons because it is light and unreactive?

Helium
Argon
Neon
Krypton

Helium

Explication

Helium is used in balloons because it is very unreactive and has a low density. Neon is more commonly used in advertising signs, and argon is often used in light bulbs.

9. What is the mass number of an atom with 12 protons and 14 neutrons?

28
26
12
14

26

Explication

Mass number is the total number of protons plus neutrons. Here, 12 + 14 = 26.

10. What happens when a more reactive halogen displaces a less reactive halogen from a halide solution?

The more reactive halogen pushes out the less reactive halogen to form a new salt and the free halogen
The more reactive halogen is replaced by the less reactive halogen
A new metal halide is formed and no halogen is released
Both halogens stay in solution without any change

The more reactive halogen pushes out the less reactive halogen to form a new salt and the free halogen

Explication

In halogen displacement, a more reactive halogen displaces a less reactive one from its salt solution. The result is a new halide salt and the displaced halogen is released.

11. Why are noble gases generally very unreactive?

Their atoms have full outer electron shells
They easily gain electrons to form negative ions
They contain no neutrons in their atoms
They are all liquids at room temperature

Their atoms have full outer electron shells

Explication

Noble gases are inert because their outer electron shells are full, so they have little tendency to gain or lose electrons. That full shell makes them very unreactive under normal conditions.

12. Which flame colour is produced by potassium ions in a flame test?

Red
Green
Yellow-orange
Lilac

Lilac

Explication

Potassium ions give a lilac flame in the flame colour test. Yellow-orange is the characteristic flame for sodium ions.

13. What is relative atomic mass of an element?

The mass number of its most common isotope
The number of protons plus electrons in an atom
The weighted average mass of its atoms, accounting for isotopes and their abundances
The total mass of all atoms in one mole of the element

The weighted average mass of its atoms, accounting for isotopes and their abundances

Explication

Relative atomic mass is a weighted average based on the masses of the isotopes and how abundant they are. It is not just the mass number of one isotope.

14. Which ion is identified by a white precipitate after adding dilute nitric acid followed by silver nitrate solution?

Sodium ions
Chloride ions
Iodide ions
Bromide ions

Chloride ions

Explication

Chloride ions form a white precipitate of silver chloride, AgCl, in the silver nitrate test. Sodium ions are not identified by this test.

15. What is the correct formula for magnesium chloride?

Mg2Cl2
MgCl
Mg2Cl
MgCl2

MgCl2

Explication

Magnesium forms Mg2+ ions and chloride forms Cl- ions, so two chloride ions are needed to balance one magnesium ion. The neutral formula is MgCl2.

16. Why do elements in the same group have similar chemical properties?

They have the same relative atomic mass
They have the same number of occupied shells
They have the same number of outer-shell electrons
They have the same atomic number

They have the same number of outer-shell electrons

Explication

Elements in the same group have the same number of electrons in their outer shell, so they tend to react in similar ways. The atomic number and relative atomic mass can be different.

Révisez avec les flashcards

Mémorisez les réponses avec 40 flashcards sur Introduction to Atomic and Periodic Chemistry.

Atomic nucleus — contents?

Protons and neutrons.

Isotopes — same?

Same element, different neutrons.

Mass number — sum?

Protons plus neutrons.

Voir les flashcards →

Approfondir avec la fiche

Consultez la fiche de révision complète sur Introduction to Atomic and Periodic Chemistry.

Voir la fiche →

Cours similaires

Gel pour les veines

Grandeurs composées et conversions

Mathématiques

Réciproque de Pythagore

Mathématiques

Réussir ses études efficacement

Les émotions humaines

The Gift of Personality

Crée tes propres QCM

Importe ton cours et l'IA génère des QCM avec corrections en 30 secondes.

Générateur de QCM