Chapter 2

Neutron

- Slightly more mass than a proton -No charge (neutral) -If neutrons are too many or too few, the nucleus may break up

First Shell

- Spherical - Closer to the nucleus than second shell - Lower energy than second shell - Can hold 2 electrons

This atom can form up to _____ single covalent bond(s).

4 There are four electrons in the outermost electron shell.

Which of these figures correctly illustrates the nature of the bonding of H2O?

4th option Oxygen is more electronegative than hydrogen.

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

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

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.

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.

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

The number of electrons in the outermost electron shell

Which of these relationships is true of an uncharged atom?

The number of protons is equal to the number of electrons

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 nonpolar. Yes! When two atoms of the same kind form a covalent bond, they share electrons equally because their electronegativity is the same.

Can electrons move between shells?

Yes, but the atom must gain or lose a quantum of energy, the exact energy difference between the shells. Light or a collision between atoms can provide energy. In the ground state, all electrons are as close to the nucleus as possible. If an electron gains a quantum of energy and moves to a shell farther from the nucleus, the atom is temporarily in an excited state.

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.

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.

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.

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.

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

A. C-H B. C-S C. O-N D. H-N E. S-H Right! N and H differ in electronegativity more than any other bonded pair of atoms in the list, making the N-H bond most polar.

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

A. O-N B. O-H C. N-H D. O-C E. C-H Yes! O and H are at opposite ends of the electronegativity scale, so the polarity is very large.

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.

What type of bond is joining the two hydrogen atoms?

Covalent A covalent bond is one in which electron pairs are shared.

Isotopes

- Isotopes are identified by mass number (protons + neutrons) - Most common isotope of carbon has mass number 12 -Symbolized as ^12 C -Has 6 neutrons -Very stable nucleus -Adding a neutron will convert ^12C to ^13C

Nucleus

- Lies at the center of the. atom - Contains protons and neutrons - Contains nearly all of the atom's mass - Number of protons is the atomic number - Number of protons plus neutrons is the mass number - Positive charge; attracts electrons

Electron

- Mass about 2000 times less than a proton - Has one unit of negative (-) charge - Attracted to the nucleus; repelled by other electrons - Continuous rapid motion - Electrons define the size of an atom

Second Shell

- Spherical - Farther from the nucleus than first cell - Higher energy than first shell - Can hold 8 electrons - Usually empty until the first shell fills

Which statement is true of the atom shown in the diagram?

- The atom is in the excited state. - The atom has more than one valence electron. - An electron will move from the outer to the inner shell. The atom has a vacancy in its inner shell; an electron has moved to the outer (valence) shell. The result is an unstable excited state. An electron will move back to the inner shell, restoring the ground state as the atom gives off energy.

Proton

-Has one unit of atomic mass -Has one unit of positive (+) charge -The number of protons determines an atom's chemical identity -Attracts electrons and repels other protons -Strong binding force holds protons in nucleus

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.

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

2

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

Double covalent The oxygen atoms are sharing two pairs of electrons.

Do all radioactive isotopes give off electrons?

Each kind of radioactive isotope has characteristic decay products, which may include electrons (called beta particles), neutrons, or photons (particles of light). Some radioactive nuclei break into two nuclei of different elements. For example, one kind of uranium isotope breaks into a helium nucleus (called an alpha particle) and a thorium nucleus

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.

The brackets are indicating a(n) _____ bond.

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

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.

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

Ionic Sodium and chlorine ions are attracted to each other.

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

O, N, C, H Congratulations! Remember this, and you'll be able to predict polarity when molecules have O or N linked to C or H.

What's potential energy?

Potential energy is due to the arrangement of objects that attract or repel one another. An arrangement has potential energy if it has a tendency to change spontaneously. The platform held by this crane is an example; if the cable breaks, the platform will fall. As the arrangement changes, potential energy becomes kinetic energy (energy of motion).

Which model most accurately represents the current view of the structure of the atom?

Probability model We cannot determine the exact motion of electrons. We can only compute the regions where electrons occur most of the time. To emphasize the uncertainty, a diagram showing random motion is more suitable than planetary paths.

Chemists assign atoms to chemical elements by counting their ________.

Protons 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. Isotopes of the same element vary in the number of neutrons in the nucleus of the atom.

Why are protons so important?

Protons determine the chemical identity of an atom 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 their numbers vary. Despite very different chemical behavior, the atom and the ion shown below are both lithium because they have three protons in the nucleus

What are the three kinds of subatomic particles containing in atoms?

Protons, neutrons and electrons Protons and neutrons make up the atom's central nucleus. Electrons move around the nucleus.

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.

Are isotopes dangerous?

Stable isotopes, such as 13C, are harmless. Radioactive isotopes are dangerous because they release high-energy particles that can damage cells. Radioactive strontium (90Sr) lodges in the bones and damages cells that make white blood cells, causing leukemia. Such hazards are the reason why safety is so important at nuclear power plants

How are electrons arranged in life's most common elements?

The "big four" elements in living systems (H, C, N, and O) are small atoms that can fit all their electrons into the first two electron shells, with room to spare. They tend to fill the valence shell by sharing with other atoms, as you'll see in the lesson on covalent bonding.

Which atom in the pictured molecule will have the strongest partial positive charge?

The C that's in C=O This C atom is bound to the two most electronegative atoms in the molecule (O), both of which are pulling electrons from C.

What's a valence shell?

The outermost shell that has electrons is called the valence shell. The electrons in the valence shell determine the atom's behavior by interacting with other atoms. Atoms have a strong tendency to fill the valence shell with electrons. They often fill it by sharing electrons with other atoms, as described in the lesson on covalent bonds.

How are isotopes used in medicine?

To cure cancer, radioactive isotopes may be inserted into tumors, where their decay kills cells. Other isotopes are used to test for disease in specific organs, using a scanner that can detect patterns of radioactive decay. Here you see a brain scan of a person who has suffered a stroke.

What's an orbital?

Within a shell, electrons occupy regions called orbitals. Each orbital can hold two electrons. Electrons in an orbital can be anywhere in space at any moment, but they spend 90% of their time in a region with a definite shape. Orbital shapes change when atoms bind in molecules. First Shell, 1s Orbital -One spherical orbital, centered on nucleus -Smallest orbital, closest to nucleus -Can hold 0, 1, or 2 electrons Second Shell, 2s Orbital -One spherical orbital, centered on nucleus -Larger than 1s orbital -Overlaps the 1s orbital -Can hold 0, 1, or 2 electrons Second Shell, 2p Orbitals - There are three of these orbitals -Each 2p orbital is dumbbell-shaped, centered on nucleus -The 2p orbitals are at mutual right angles(x,y, and z axes) -Each orbital extends to nucleus, overlapping 1s and 2s orbitals -Each can hold 0, 1, or 2 electrons Both Shells - First shell has one orbital - Second shell has four orbitals - Orbitals of second shell are larger than orbitals of first shell - All of the orbitals overlap

An ionic bond involves _____.

an attraction between ions of opposite charge. This is the definition of an ionic bond.

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

are different ions Ions are charged atoms.

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

electron-sharing Good choice! Only in covalent bonds do atoms share electrons. Return to Assignment

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.

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