$$6.02 \times 10$$^{23}$$ molecules

Question 1

Which of the following statements best explains why elements form compounds according to the octet rule?

Accepted Answer

Elements form compounds to achieve a stable arrangement of eight electrons in their valence shell.

Question 2

How many electrons can be held in the third energy level ($$n = 3) of an $$atom?

Accepted Answer

$$18$$

Question 3

Which of the following ions is isoelectronic with neon ($$\mathrm{Ne}$$)?

Accepted Answer

$$\mathrm{Na^+}$$

Question 4

A sample contains $$12.04 	imes 10$$^{23}$$ atoms of magnesium. How many moles of magnesium are present?

Accepted Answer

$$2$$ moles

Question 5

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

Accepted Answer

$$\mathrm{NaCl}$$

Question 6

What is the correct name for the compound $$\mathrm{$$FeCl_3$$}$$?

Accepted Answer

Iron(III) chloride

Question 7

Which of the following best describes the shape of a methane ($$\mathrm{CH_4$}) $$molecule according to VSEPR theory?

Accepted Answer

Tetrahedral

Question 8

What is the molar mass of $$\mathrm{$$MgSO_4$$}$$? (Atomic masses: $$\mathrm{Mg} = 24.3$$, $$\mathrm{S} = 32.1$$, $$\mathrm{O} = 16.0)$$

Accepted Answer

$$120.4 g/$$mol

Question 9

Which of the following molecules is nonpolar despite having polar bonds?

Accepted Answer

$$\mathrm{CO_2$}$$

Question 10

What is the formula for diphosphorus pentoxide?

Accepted Answer

$$\mathrm{P_2O_5}$$

Question 11

Which of the following statements about electronegativity is correct?

Accepted Answer

Fluorine is the most electronegative element.

Question 12

A bond between which pair of elements is most likely to be ionic?

Accepted Answer

Sodium and chlorine

Question 13

How many valence electrons are present in a silicon ($$\mathrm{Si}) $$atom?

Accepted Answer

$$4$$

Question 14

Which of the following best describes the electron arrangement in the second energy level ($$n = 2$$)?

Accepted Answer

It can hold a maximum of $$8$$ electrons.

Question 15

What is the correct name for $$\mathrm{N_2O_4}$$?

Accepted Answer

Dinitrogen tetroxide

Question 16

Which of the following best explains why water ($$\mathrm{H_2O}) is a $$polar molecule?

Accepted Answer

It has polar bonds and a bent molecular shape.

Question 17

A sample of $$18.0$$ grams of water ($$\mathrm{H_2O}) $$contains how many molecules? (Molar mass of $$\mathrm{H_2O} = 18.0 g/$$mol)

Accepted Answer

$$6.02 	imes 10$$^{23}$$ molecules

Question 18

Which of the following is the correct Lewis structure for methane ($$\mathrm{CH_4$}$$)?

Accepted Answer

A central carbon atom with four single bonds to four hydrogen atoms.

Question 19

Which of the following best describes a polyatomic ion?

Accepted Answer

A group of nonmetals that form an ion with a net charge.

Question 20

What is the correct formula for the ionic compound formed between calcium and phosphate?

Accepted Answer

$$\mathrm{Ca_3$(PO_4$)_2}$$

Chapter 3 Study Notes: Compounds—How Elements Combine (GOB Chemistry)

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