$$(6 \times 12) + (12 \times 1) + (6 \times 16) = 180$$

Question 1

Which of the following statements best explains why oxygen (O) and hydrogen (H) atoms combine to form water (H$$_2O) $$molecules?

Accepted Answer

Oxygen and hydrogen atoms combine to achieve stable electron configurations by sharing electrons, forming covalent bonds.

Question 2

Which of the following best describes the difference between atomic number and mass number?

Accepted Answer

Atomic number is the number of protons in an atom, while mass number is the sum of protons and neutrons.

Question 3

A neutral atom of sodium (Na) has an atomic number of 11 and a mass number of 23. How many neutrons does it have?

Accepted Answer

$$23 - 11 = 12$$ neutrons

Question 4

Which of the following best describes a polar covalent bond?

Accepted Answer

A bond in which electrons are shared unequally between two atoms due to a difference in electronegativity.

Question 5

Which of the following elements is a trace element essential for human life?

Accepted Answer

Iron (Fe)

Question 6

Given the electron configuration of an atom, how many electrons are required to fill the second energy level (shell)?

Accepted Answer

8 electrons

Question 7

Which of the following best explains why noble gases are chemically inert?

Accepted Answer

They have full valence electron shells, making them stable and unlikely to react.

Question 8

A molecule of methane (CH$$_4) $$contains which type of covalent bonds?

Accepted Answer

Four single covalent bonds

Question 9

Which of the following best describes a hydrogen bond?

Accepted Answer

A weak attraction between a hydrogen atom covalently bonded to an electronegative atom and another electronegative atom.

Question 10

Which of the following is the correct molecular weight of glucose (C$$_6H$_{12}O$_6$$)? (Atomic weights: C = 12, H = 1, O = 16)

Accepted Answer

$$(6 	imes 12) + (12 	imes 1) + (6 	imes 16) = 180$$

Question 11

Which of the following best distinguishes between a molecule and a compound?

Accepted Answer

A molecule is a group of two or more atoms held together by covalent bonds, while a compound contains atoms of two or more different elements.

Question 12

Which of the following best describes a reversible chemical reaction at equilibrium?

Accepted Answer

The rate of the forward reaction equals the rate of the reverse reaction, so the concentrations of reactants and products remain constant.

Question 13

Which of the following is the best example of an ionic compound?

Accepted Answer

NaCl

Question 14

If an atom has 17 protons, 18 neutrons, and 17 electrons, what is its atomic number and mass number?

Accepted Answer

Atomic number = 17, Mass number = 35

Question 15

Which of the following best describes the role of valence electrons in chemical bonding?

Accepted Answer

Valence electrons are the electrons in the outermost shell and are involved in forming chemical bonds.

Question 16

Which of the following statements about isotopes is correct?

Accepted Answer

Isotopes of an element have the same number of protons but different numbers of neutrons.

Question 17

Which of the following best explains why water (H$$_2O) is a $$polar molecule?

Accepted Answer

Oxygen is more electronegative than hydrogen, causing unequal sharing of electrons and a bent molecular shape.

Question 18

Which of the following best describes a cation?

Accepted Answer

An atom that has lost electrons and has a positive charge.

Question 19

Which of the following is the correct Lewis dot structure for a carbon atom?

Accepted Answer

A 'C' symbol with four dots around it, representing four valence electrons.

Question 20

Which of the following best describes the difference between a single, double, and triple covalent bond?

Accepted Answer

A single bond shares one pair of electrons, a double bond shares two pairs, and a triple bond shares three pairs of electrons.

The Chemical Context of Life: Study Notes for General Biology

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