Q: A radioactive isotope of Np-240 has a half-life of 1 hour. If you start with 60 grams, how much will remain after 4 hours?

$$60 \times \left(\frac{1}{2}\$$right)^4$$ = 3.75$$ grams

Question 1

Which subatomic particle is responsible for the identity of an element, and how is this reflected in the periodic table?

Accepted Answer

Protons; the number of protons is the atomic number, which identifies the element.

Question 2

A radioactive isotope of Np-240 has a half-life of 1 hour. If you start with 60 grams, how much will remain after 4 hours?

Accepted Answer

$$60 	imes \left(\frac{1}{2}\$$right)^4$$ = 3.75$$ grams

Question 3

Which of the following best describes the difference between a molecule and a compound?

Accepted Answer

A molecule consists of two or more atoms bonded together, while a compound consists of two or more different elements in a fixed ratio.

Question 4

Which of the following elements is NOT one of the four most essential elements for life?

Accepted Answer

Phosphorus

Question 5

How many electrons can the first electron shell of an atom hold?

Accepted Answer

2

Question 6

Which type of chemical bond involves the sharing of electron pairs between atoms?

Accepted Answer

Covalent bond

Question 7

What is the main difference between polar and nonpolar covalent bonds?

Accepted Answer

Polar bonds have unequal sharing of electrons due to differences in electronegativity, while nonpolar bonds share electrons equally.

Question 8

Which of the following is NOT a property of salts (ionic compounds)?

Accepted Answer

They are considered molecules.

Question 9

What is the electron configuration for a carbon atom?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^2$$

Question 10

Which intermolecular force is responsible for the ability of geckos to climb smooth surfaces?

Accepted Answer

Van der Waals interactions

Question 11

A hydrogen bond forms when a hydrogen atom covalently bonded to one electronegative atom is attracted to another electronegative atom. Which atoms are most commonly involved in hydrogen bonding in living cells?

Accepted Answer

Oxygen and nitrogen

Question 12

Which statement best describes chemical equilibrium in a reversible reaction?

Accepted Answer

The forward and reverse reactions occur at the same rate, and the relative concentrations of reactants and products do not change.

Question 13

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 14

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

Accepted Answer

They have a full valence shell of electrons.

Question 15

Which of the following is a trace element required by humans in less than 0.01% of body mass?

Accepted Answer

Iron

Question 16

What is the main reason that water molecules are polar?

Accepted Answer

Oxygen is more electronegative than hydrogen, causing unequal sharing of electrons.

Question 17

Which of the following best describes hybridization in the context of molecular shape?

Accepted Answer

Hybridization is the combination of s and p orbitals to form new, specific molecular shapes.

Question 18

Which of the following is an example of an intramolecular force?

Accepted Answer

Ionic bond

Question 19

A sodium atom loses one electron to become a sodium ion. What is the charge of the resulting ion?

Accepted Answer

$$+1$$

Question 20

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

Accepted Answer

Electrons are responsible for the formation of chemical bonds by being shared or transferred between atoms.

The Chemical Context of Life: Atoms, Elements, and Chemical Bonds

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