Chapter 2

What is matter?

Anything that takes up space and has mass. Matter is made up of elements.

Give examples of matter.

Rocks, metals, oils, gases, living organisms.

What is an element?

An element is a substance that cannot be broken down to other substances by chemical reactions.

Give examples of elements.

Examples of elements include gold, copper, carbon, and oxygen.

What is a compound?

A substance consisting of two or more different elements combined in a fixed ratio.

Give examples of a compound.

Table salt (NaCl) and Water (H2O)

What do a compound's properties depend on?

A compound's properties depend on its atoms and how they are bonded together.

What are essential elements?

They are elements that an organism needs to live a healthy life and reproduce.

What are the four elements that make up approximately 96% of living matter?

Oxygen (O), carbon (C), hydrogen (H), and nitrogen (N)

What are the elements that account for most of the remaining 4% of an organism's mass?

Calcium (Ca), phosphorus (P), potassium (K), sulfur (S), and a few other elements

What are trace elements?

Elements required by an organism in only minute quantities

Give an example of a trace element needed by all forms of life.

Iron (Fe)

Give an example of a trace element needed by vertebrates

Iodine (I)

What is an atom?

The smallest unit of matter that retains the properties of an element.

What are subatomic particles?

Even smaller parts that make up atoms: neutrons, protons, and electrons

What is the charge of a proton?

Protons are electrically positive.

What is the charge of a electron?

Electrons are electrically negative.

What is the charge of a neutron?

Neutrons are electrically neutral.

Where are protons and neutrons located?

In the dense core, or atomic nucleus, at the center of an atom.

What charge does the atomic nucleus have?

A positive charge due to the presence of protons.

Where are electrons located?

They form a 'cloud' of negative charge around the nucleus.

What is the role of the attraction between opposite charges?

It keeps the electrons in the vicinity of the nucleus.

What is the unit of measurement used for atoms and subatomic particles?

Dalton/atomic mass unit (amu)

What is the mass of a neutron and proton in grams?

1.7 * 10^-24 g

Why do we use dalton instead of grams to describe the mass of atoms and subatomic particles?

Grams are not useful for minuscule objects

What is the mass of an electron compared to a neutron or proton?

About 1/2000

When computing the total mass of an atom, which subatomic particle can be ignored?

Electrons

What is the atomic number?

Number of protons in an atom.

Where is the atomic number written?

As a subscript to the left (bottom left) of the element symbol

What is the atomic number of helium?

2

How many protons are in an atom of helium?

2

What is the atomic mass of helium?

4

How can we determine the number of neutrons in an atom?

By subtracting the atomic number from the mass number

What is the mass number?

The total mass of an atom. Total number of protons and neutrons in an atom

Where is the mass number written?

As a superscript to the left (top left) of the element symbol

What is an isotope?

Different atomic forms of the same element with varying numbers of neutrons.

What are examples of isotope of carbon?

Carbon-12, Carbon-13, and Carbon-14

How many neutrons does carbon-12, carbon-13, and carbon-14 have?

6 neutrons, 7 neutrons, and 8 neutrons

What does it mean for an isotope to be stable?

Its nucleus does not have a tendency to lose subatomic particles.

What is a radioactive isotope?

An isotope that decays spontaneously, giving off particles and energy.

What happens when a carbon-14 atom decays?

A neutron decays into a proton, transforming the atom to an atom of a different element.

What is the process called when a nucleus decays?

Radioactive decay.

What is the term for an atom of a different element formed after radioactive decay?

A transformed atom.

Are stable isotopes prone to radioactive decay?

No, only unstable isotopes are prone to radioactive decay.

What are some useful applications of radioactive isotopes in biology?

Tracing metabolic pathways, diagnosing diseases, and studying biological processes.

What is the hazard of radiation from decaying isotopes?

Damaging cellular molecules

What does the layering of fossil beds establish?

Relative age, with deeper fossils being older

What is a parent isotope?

An isotope that decays into a daughter isotope

What is the half-life of an isotope?

The time it takes for 50% of the parent isotope to decay

What is radiometric dating used for?

Determining the age of fossils or rocks

How do scientists calculate the age using radiometric dating?

By measuring the ratio of different isotopes and counting the number of half-lives

What is the electron's role in chemical reactions?

Electrons are directly involved in chemical reactions.

What is energy?

The capacity to cause change.

What is potential energy?

Energy that matter possesses due to its location or structure.

Give an example of potential energy.

Water in a reservoir on a hill because of its altitude.

What is the natural tendency of matter in terms of potential energy?

To move towards the lowest possible state of potential energy.

What is an electron's energy level correlated with?

Average distance from the nucleus.

What are electron shells?

Different energy levels with characteristic average distances.

How are shells represented in diagrams?

Concentric circles.

Which shell is closest to the nucleus?

The first shell.

Do electrons in the first shell have high or low potential energy?

Lowest potential energy.

Do electrons in the second shell have high or low potential energy?

More energy than the first shell.

Do electrons in the third shell have high or low potential energy?

Even more energy than the second shell.

What is required for an electron to move from one shell to another?

Absorbing or losing an amount of energy equal to the difference in potential energy between the shells.

What happens when an electron absorbs energy?

It moves to a shell farther out from the nucleus.

What happens when an electron loses energy?

It falls back to a shell closer to the nucleus.

What is usually released when an electron loses energy?

Visible light or ultraviolet radiation.

What determines the chemical behavior of an atom?

Distribution of electrons in the atom's electron shells.

How can we build atoms of other elements?

By adding 1 proton and 1 electron at a time (with neutrons).

What is the valence shell?

The outermost electron shell of an atom.

What are valence electrons?

Electrons in the outermost shell of an atom.

What is the significance of valence electrons?

They determine the chemical behavior of an atom.

What is the chemical behavior of atoms with the same number of valence electrons?

They exhibit similar chemical behavior.

Give an example of two elements with the same number of valence electrons.

Fluorine (F) and chlorine (Cl).

What is the chemical behavior of an atom with a completed valence shell?

It is unreactive and does not readily interact with other atoms.

Which elements in the periodic table have full valence shells?

Helium, neon, and argon.

What does each electron shell contain?

Electrons at a particular energy level.

How are electrons distributed within an electron shell?

Among a specific number of orbitals.

What is an orbital?

A component of an electron shell.

How many orbitals does the first electron shell have?

One spherical s orbital (1s).

How many orbitals does the second electron shell have?

One large spherical s orbital (2s) and three dumbbell-shaped p orbitals (2p).

How many electrons can occupy a single orbital?

2

How many electrons can the first electron shell accommodate in its s orbital?

2

How many electrons can the four orbitals of the second electron shell hold?

8; 2 in each orbital

What is the reactivity of an atom?

It arises from the presence of unpaired electrons in the atom's valence shell.

How do atoms combine to form molecules and ionic compounds?

Atoms with incomplete valence shells can interact with certain other atoms to share or transfer valence electrons to completes its valence shell.

What are the attractions that hold atoms close together?

Chemical bonds.

What is a covalent bond?

It is the sharing of a pair of valence electrons by two atoms.

What is a single bond?

A single covalent bond; the sharing of a pair of valence electrons by two atoms.

What is a double bond?

When two pairs of valence electrons are shared between two atoms

What is bonding capacity?

Number of covalent bonds an atom can form.

What is valence?

Atom's bonding capacity and number of electrons required to complete its outermost shell.

What is the valence of hydrogen?

What is the valence of oxygen?

What is the valence of nitrogen?

What is the valence of carbon?

What is electronegativity?

Attraction of an atom for shared bonding electrons.

What is a nonpolar covalent bond?

Covalent bond between two atoms of the same element with equal electronegativity.

What is a polar covalent bond?

Covalent bond between atoms with different electronegativity.

What determines the polarity of a polar covalent bond?

Relative electronegativity of the two atoms.