Unit 1

Question 1

What is science?

Answer 1

The study of the physical and natural world through observations and experiments.

Question 2

What is chemistry?

Answer 2

The study of matter and its transformations. Matter is composed of atoms.

Question 3

State the main points of Dalton’s atomic theory.

Answer 3

1. Matter is composed of atoms.
2. Elements consist of one type of atom.
3. Atoms of one element differ from others.
4. Compounds consist of atoms in whole-number ratios.
5. Atoms are not created or destroyed in a chemical change

Question 4

What law does Dalton’s atomic theory support?

Answer 4

Law of conservation of matter, constant composition, and multiple proportions.

Question 5

Who discovered the electron?

Answer 5

A: J.J. Thomson through the cathode ray tube experiment.

Question 6

Q: What are the three conclusions of Thomson’s experiment?

Answer 6

A:
1. Electrons are negatively charged particles.
2. They are smaller than atoms.
3. Electrons are the same for all elements.

Question 7

Q: What was Millikan’s contribution to atomic theory?

Answer 7

A: He measured the charge of the electron using the oil drop experiment.

Question 8

Q: What did Rutherford’s alpha scattering experiment demonstrate?

Answer 8

A: It led to the discovery of the nucleus, proving the atom has a dense, positively charged center.

Question 9

Q: What are the charges and masses of protons, neutrons, and electrons?

Answer 9

A:
- Proton: +1, 1.67 × 10⁻²⁷ kg
- Neutron: 0, 1.67 × 10⁻²⁷ kg
- Electron: -1, 9.11 × 10⁻³¹ kg

Question 10

Q: What are isotopes?

Answer 10

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

Question 11

Q: Define ions.

Answer 11

A: Atoms or groups of atoms with a net charge due to loss or gain of electrons.

Question 12

Q: What is a cation?

Answer 12

A: A positively charged ion (loses electrons).

Question 13

Q: What is an anion?

Answer 13

A: A negatively charged ion (gains electrons).

Question 14

Q: What is a chemical symbol?

Answer 14

A: A notation of one or two letters representing an element (e.g., H for hydrogen).

Question 15

Q: How do you calculate mass number?

Answer 15

A: Mass number = protons + neutrons.

Question 16

Q: What are ionic compounds?

Answer 16

A: Compounds formed by the combination of metal and non-metal ions.

Question 17

Q: Name the compound: FeCl₃.

Answer 17

A: Iron (III) chloride.

Question 18

Q: What are covalent compounds?

Answer 18

A: Compounds formed between non-metals through shared electrons.

Question 19

Q: Name the compound: N₂O.

Answer 19

A: Dinitrogen monoxide.

Question 20

Q: Define binary acids.

Answer 20

A: Acids containing hydrogen and one non-metal, named with the “hydro-ic” suffix.

Question 21

Q: What is Planck’s equation?

Answer 21

A: E = hν, where h = Planck’s constant and ν = frequency.

Question 22

Q: State Planck’s constant.

Answer 22

A: 6.626 × 10⁻³⁴ Js.

Question 23

Q: What is the photoelectric effect?

Answer 23

A: Emission of electrons from a metal when light of sufficient frequency shines on it.

Question 24

Q: What is the threshold frequency?

Answer 24

A: The minimum frequency needed to eject electrons in the photoelectric effect.

Question 25

**Q:** Who proposed the Bohr model of the atom?

Answer 25

**A:** Niels Bohr in 1913.

Question 26

**Q:** State Bohr's postulates.

Answer 26

**A:** Electrons orbit in stationary states and emit/absorb energy when transitioning between levels.

Question 27

**Q:** What is the Rydberg constant?

Answer 27

**A:** 2.179 × 10⁻¹⁸ J.

Question 28

**Q:** Define quantum numbers.

Answer 28

**A:** Numbers describing an electron's position: n, l, ml, ms.

Question 29

**Q:** What does the principal quantum number (n) define?

Answer 29

**A:** The size and energy of an orbital.

Question 30

**Q:** What does the angular momentum quantum number (l) define?

Answer 30

**A:** The shape of the orbital (s, p, d, f).

Question 31

**Q:** What are degenerate orbitals?

Answer 31

**A:** Orbitals with the same energy.

Question 32

**Q:** What does Heisenberg's uncertainty principle state?

Answer 32

**A:** It is impossible to know both the position and momentum of a particle simultaneously.

Question 33

**Q:** What is an orbital?

Answer 33

**A:** A region in space where the probability of finding an electron is highest.

Question 34

**Q:** State Pauli’s exclusion principle.

Answer 34

**A:** No two electrons in an atom can have the same set of four quantum numbers.

Question 35

**Q:** What is Hund's rule?

Answer 35

**A:** Electrons occupy degenerate orbitals singly before pairing.

Question 36

**Q:** What is the Aufbau principle?

Answer 36

**A:** Electrons fill orbitals starting with the lowest energy level.

Question 37

**Q:** What is electronic configuration?

Answer 37

**A:** Distribution of electrons in orbitals of an atom.

Question 38

**Q:** Write the electronic configuration for Fe²⁺.

Answer 38

**A:** [Ar] 3d⁶.

Question 39

**Q:** How does atomic size change across a period?

Answer 39

**A:** It decreases.

Question 40

**Q:** How does atomic size change down a group?

Answer 40

**A:** It increases.

Question 41

**Q:** Define ionization energy.

Answer 41

**A:** The energy required to remove an electron from an atom in the gaseous state.

Question 42

**Q:** How does ionization energy change across a period?

Answer 42

**A:** It increases.

Question 43

**Q:** What is electron affinity?

Answer 43

**A:** The energy change when an atom gains an electron.

Question 44

**Q:** Define shielding effect.

Answer 44

**A:** Inner electrons shield outer electrons from nuclear attraction.

Question 45

**Q:** What are acidic oxides?

Answer 45

**A:** Oxides of non-metals that react with water to form acids.

Question 46

**Q:** What are basic oxides?

Answer 46

**A:** Oxides of metals that react with water to form bases.

Question 47

**Q:** What are amphoteric oxides?

Answer 47

**A:** Oxides that react with both acids and bases (e.g., Al₂O₃).

Question 48

**Q:** What is a reducing agent?

Answer 48

**A:** A substance that donates electrons in a reaction.

Question 49

**Q:** What is the flame color of lithium?

Answer 49

**A:** Red.

Question 50

**Q:** Why don’t Mg and Be produce flame colors?

Answer 50

**A:** Their electrons require too much energy to excite.