The Chemical Context of Life

How many electrons are involved in a single covalent bond?

2

The innermost electron shell of an atom can hold up to _____ electrons.

2 This is the maximum number of electrons that can occupy the innermost electron shell

How many electrons are involved in a double covalent bond?

4

The atomic number of nitrogen is 7. Nitrogen-15 has a greater mass number than nitrogen-14 because the atomic nucleus of nitrogen-15 contains _____.

8 neutrons

The mass number of an atom is 15, and its atomic number is 7. The atom probably has...

8 neutrons in the nucleus. The atomic number (7) gives the number of protons, and the mass number is the number of protons plus neutrons.

true of all atoms that are anions?

The atom has more electrons than protons.

Which of the following statements about electrons is false?

The electron is electrically neutral.

Dr. Haxton says the O-O bond is polar and the C-C bond is nonpolar. A good student would say ..

Wrong again, Ralph. Both bonds are non polar. When two atoms of the same kind form a covalent bond, they share electrons equally because their electronegativity is the same

A phrase that applies to covalent bonding and not other kinds of bonds is ...

electron-sharing. Only in covalent bonds do atoms share electrons

In a double covalent bond, a carbon atom shares ...

electrons in two orbitals. A double bond involves two orbitals, each with a shared pair of electrons

Covalent bonds hold atoms together because they ...

fill shells without giving atoms much charge. bring electrons closer to protons. Electron-sharing brings electrons closer to nuclei and it fills shells without giving the atoms much charge. Both factors stabilize the bond.

What name is given to the bond between water molecules?

hydrogen A hydrogen atom with a net positive charge is attracted to an oxygen atom with a net negative charge.

Water molecules are attracted to one another by _____.

hydrogen bonds

In salt, what is the nature of the bond between sodium and chlorine?

ionic Sodium and chlorine ions are attracted to each other.

oxygen

is more electronegative than hydrogen

A(n) _____ refers to two or more atoms held together by covalent bonds.

molecule A molecule is defined as two or more atoms held together by covalent bonds

Bonds between two atoms that are equally electronegative are _____.

nonpolar covalent bonds

Compared with 31P, the radioactive isotope 32P has

one more neutron.

A covalent bond is likely to be polar when _____.

one of the atoms sharing electrons is more electronegative than the other atom

A covalent chemical bond is one in which _____.

outer-shell electrons of two atoms are shared so as to satisfactorily fill their respective orbitals

Dr. Jones says an atom has 3 electrons in the first shell and four electrons in the second shell. Someone should tell Dr. Jones that ...

the first shell shouldn't have 3 electrons. The first shell can only have 0, 1, or 2 electrons.

Based on electron configuration, which of the elements in the figure above would exhibit a chemical behavior most like that of oxygen?

sulfur

electron

symbol e -1 charge mass of ~1/2000 amu the electron mass is only about 5.5×10−4amu.

neutron

symbol n 0 charge mass ~ 1amu

proton

symbol p +1 charge mass ~ 1amu

In the term trace element, the adjective trace means that

the element is required in very small amounts.

The reactivity of an atom arises from

the existence of unpaired electrons in the valence shell.

An electrically neutral molecule has the formula C3H4O2N. If the carbon atoms form the usual number of bonds, how many covalent bonds will each hydrogen atom have with other atoms in the molecule?

1

Fluorine's atomic number is 9 and its atomic mass is 19. How many neutrons does fluorine have?

10 Atomic mass is equal to the number of protons plus the number of neutrons (19-9 = 10)

An atom has 8 protons, 8 neutrons, and 8 electrons. Another isotope of the same element might have ...

10 neutrons Isotopes have the same number of protons; different numbers of neutrons.

Choose the correct balanced equation for the following reaction. C8H18 + O2 → CO2 + H2O

2 C8H18 + 25 O2 → 16 CO2 + 18 H2O This equation has every element balanced and has the smallest possible whole number coefficients.

To fill the valence shell, an electrically neutral, unbonded atom with atomic number 8 must add ...

2 electrons. The neutral atom has 8 electrons. Two electrons fill the first shell, and 6 go into the second (valence) shell. Two more electrons would fill the valence shell.

An atom's atomic number is 7. Its valence is most likely ...

3 The neutral atom has 7 electrons. Two electrons fill the first shell, and 5 go into the second (valence) shell. The atom needs 3 more electrons to fill the valence shell.

In molecules, C, H, O, and N atoms usually make __, __, __, and __ bonds respectively.

4,1,2,3

An uncharged atom of boron has an atomic number of 5 and an atomic mass of 11. How many protons does boron have?

5 The atomic number is equal to the number of protons.

How many electrons will a single atom of sulfur with no charge and no bonds have in its valence shell

6

What is the atomic number of an atom that has 6 protons, 6 neutrons, and 6 electrons?

6 This is an atom of carbon, an element with 6 protons. Atomic number is the number of protons in an atom.

A positive ion with two units of charge has 10 neutrons and 8 protons. The ion also has ...

6 electrons.

What happens when two atoms form a chemical bond?

A chemical bond forms when two atoms transfer or share outer electrons to complete their outer shells. Only the electrons of atoms participate in chemical bonds, which form when atoms transfer or share outer or valence electrons.

ATOMS

All matter is made up of atoms. An atom has a nucleus consisting of positively charged protons and uncharged neutrons. Negatively charged electrons are found outside of the nucleus of the atom.

Two C atoms form a double bond. Each C is bound to two H atoms. Which statement is true?

All the atoms lie in a plane. The double bond limits all the atoms to a plane.

Which statement about relative potential energy of electrons is correct?

An electron in the 3 p orbital of the third electron shell has more potential energy than an electron in the 2 p orbital of the second electron shell.

What does the term electron orbital describe?

An electron orbital describes a three-dimensional space where an electron can be found 90% of the time. We cannot know the exact location of an electron. Instead, we can describe a three-dimensional space in which an electron spends most of its time.

Choose the appropriate balanced equation for the following chemical reaction. C6H6 + H2 → C6H12

C6H6 + 3 H2 → C6H12 You balanced the equation appropriately by making sure that the same quantity of each element appears on both sides of the arrow.

An atom has 6 electrons, 6 protons, and 6 neutrons. You can tell that this atom belongs to the element _____ because _____________________.

C; it has 6 protons. Atoms represent the element carbon (C) if they have six protons.

Which statement is true of atoms?

Electrons determine the atom's size. With electrons on the surface, atoms repel one another when they come too close. Thus, electrons determine the space that an atom occupies.

Which statement about the following reaction is true? 4 Fe + 3 O2 → 2 Fe2O3

Four atoms of Fe react with 3 molecules of O2 to form 2 molecules of Fe2O3 You identified the reactants as Fe and O and the product as Fe2O3. You also knew that the coefficients in the equation correspond to the number of atoms or molecules that take part in the reaction.

If you want a molecule that is highly polar, look for one that contains:

H-N N and H differ in electronegativity more than any other bonded pair of atoms in the list, making the N-H bond most polar.

Which of the following are compounds?

H2O and CH4,

The atomic number of sulfur is 16. Sulfur combines with hydrogen by covalent bonding to form a compound, hydrogen sulfide. Based on the number of valence electrons in a sulfur atom, predict the molecular formula of the compound.

H2S

If an atom has a charge of +1, which of the following must be true?

It has one more proton than it does electrons.

Which statement is most useful in explaining why chemists assign atoms to chemical elements by counting protons?

None of these. Elements are defined by the number of protons. Protons give an enduring basis for atomic behavior because they are permanently anchored in the nucleus, where their attraction determines how many electrons the atom can hold. By contrast, electrons come and go, and the numbers vary.

Which answer correctly ranks the atoms in terms of decreasing electronegativity (the highest electronegativity first)?

O, N, C, H

Use your knowledge of electronegativity to pick out the most polar bond in the list below.

O-H O and H are at opposite ends of the electronegativity scale, so the polarity is very large

By making two covalent bonds, an O atom (with 8 protons) fills its valence shell. Why does the atom's charge stay close to zero?

Shared electrons aren't always near oxygen Oxygen keeps 6 electrons to itself. The 4 shared electrons migrate between O and the other atoms, thus contributing 4 half-charges to oxygen. This gives oxygen about 8 units of negative charge, balancing the atom's 8 protons.

Which of the following statements about neutrons is false?

The neutron is positively charged.

Which of these relationships is true of an uncharged atom?

The number of protons is equal to the number of electrons In this situation the number of positive charges is equal to the number of negative charges.

Which of the following statements about protons is false?

The proton is found outside the nucleus of an atom.

Which of the following statements correctly describes any chemical reaction that has reached equilibrium?

The rates of the forward and reverse reactions are equal.

Which statement is true of the energy levels of electrons in shells?

The valence shell has higher energy than other occupied shells. The outer occupied shell is the valence shell, and outer shells hold electrons at higher energy than inner shells.

Which answer helps to explain why carbon atoms tend to make 4 covalent bonds?

The valence shell needs 8 electrons. Without help, C can only hold 4 electrons in the valence shell. To fill the shell, 4 more electrons must be shared, making 4 covalent bonds.

Which of these refers to atoms with the same atomic number but different atomic masses?

These atoms are isotopes. Atoms with the same atomic number and different atomic masses are referred to as isotopes.

True or false: Ions may form by transferring an atomic nucleus (with or without electrons) to another molecule.

True Correct! For example, a hydrogen nucleus (H+) may move between two water molecules, making an H3O+ ion and an OH- ion

Which of the following bonds can form between atoms of equal electronegativity?

Van der Waals interactions can form between atoms of equal electronegativity. Even nonpolar covalent bonds have temporary regions of partial positive and negative charge, due to the chance movements of electrons. Attractions between such transient positive and negative charges create weak Van der Waals interactions.

Which statement about weak bonds is correct?

Weak bonds are transient and easily reversible. Molecules that form weak bonds can come together, interact, and then separate. The combined effect of many weak and transient hydrogen bonds or Van der Waals interactions can produce important emergent properties. Read about the importance of the transience of weak bonds such as hydrogen bonds, ionic bonds, and Van der Waals interactions.

Fluorine has an atomic number of 9. Which of the following would you do to a neutral fluorine atom to complete its valence shell?

add 1 electron

Radioactive decay is likely to occur when ...

an atom has too many neutrons. The atomic nucleus becomes unstable if the ratio of protons to neutrons is too far from unity.

An ionic bond involves _____.

an attraction between ions of opposite charge

Atoms with the same number of protons but with different electrical charges _____.

are different ions Ions are charged atoms.

Partial charges occur when ...

atoms share electrons unequally. Each kind of atom has a different attraction for electrons. Thus, atoms of different kinds share electrons unequally. That gives one atom a partial negative charge; the other atom a partial positive charge.

A(n) _____ bond joins these two oxygen atoms.

double covalent

Compared to covalent bonds, ionic bonds ...

rely much less on electron-sharing. Covalent bonds are entirely based on sharing electrons, whereas ionic bonds are attractions between ions that keep their electrons.

What type of bond joins the carbon atom to each of the hydrogen atoms?

single (nonpolar) covalent Each carbon-hydrogen bond involves a single pair of equally shared electrons

An atom has four electrons in its valence shell. What types of covalent bonds is it capable of forming?

single, double, or triple

What determines the types of chemical reactions that an atom participates in?

the number of electrons in the outermost electron shell An atom is least likely to participate in a reaction when its outermost shell is stable.

Two atoms always represent the same element if they have ...

the same number of protons. The number of protons defines a chemical element. The number of neutrons and electrons can differ among atoms of the same element.