Unit 1.2: the chemistry of life

Matter

Anything that takes up space and has mass

Element

A substance that cannot be broken down into other substances by chemical reactions

Compound

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

Emergent properties of compounds

A compound has properties that are different from the properties of the individual elements that make it up

Essential elements

Elements that an organism needs to live a healthy life and reproduce

Four elements that make up most living matter

Oxygen, carbon, hydrogen, and nitrogen

Percentage of living matter made of oxygen, carbon, hydrogen, and nitrogen

Approximately 96%

Oxygen in the human body

About 65.0% of body mass

Carbon in the human body

About 18.5% of body mass

Hydrogen in the human body

About 9.5% of body mass

Nitrogen in the human body

About 3.3% of body mass

Calcium in the human body

About 1.5% of body mass

Phosphorus in the human body

About 1.0% of body mass

Potassium in the human body

About 0.4% of body mass

Sulfur in the human body

About 0.3% of body mass

Sodium in the human body

About 0.2% of body mass

Chlorine in the human body

About 0.2% of body mass

Magnesium in the human body

About 0.1% of body mass

Trace elements

Elements required by an organism in only very small quantities

Examples of trace elements

Iron, iodine, boron, chromium, cobalt, copper, fluorine, manganese, molybdenum, selenium, silicon, tin, vanadium, and zinc

Atom

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

Subatomic particles

Particles smaller than an atom, including protons, neutrons, and electrons

Proton

A positively charged subatomic particle found in the atomic nucleus

Neutron

An electrically neutral subatomic particle found in the atomic nucleus

Electron

A negatively charged subatomic particle found outside the atomic nucleus

Atomic nucleus

The dense center of an atom containing protons and neutrons

What determines an atom's identity?

The number of protons it contains

Atomic number

The number of protons in the nucleus of an atom

Neutral atom

An atom with equal numbers of protons and electrons

Mass number

The total number of protons and neutrons in an atom's nucleus

How to calculate the number of neutrons

Mass number minus atomic number

Atomic mass

The total mass of an atom, measured in daltons

Dalton

A unit used to measure the mass of atoms and subatomic particles

Mass of a proton

Approximately 1 dalton

Mass of a neutron

Approximately 1 dalton

Mass of an electron

About 1/2,000 the mass of a proton or neutron

Where is most of an atom's mass located?

In the nucleus

Isotope

One of several atomic forms of the same element that have different numbers of neutrons

What stays the same among isotopes of an element?

The number of protons

What differs among isotopes of an element?

The number of neutrons and therefore their masses

Carbon

12

Carbon

13

Carbon

14

Stable isotope

An isotope whose nucleus does not spontaneously decay

Radioactive isotope

An isotope whose nucleus spontaneously decays, releasing particles and energy

Radioactive tracer

A radioactive isotope incorporated into a molecule so its movement or activity can be tracked

PET

Positron

Half

life

Radiometric dating

A method that uses isotope ratios and half

Energy

The capacity to cause change or do work

Potential energy

Energy that matter possesses because of its location or structure

Electron energy

Potential energy associated with an electron's position relative to the nucleus

Electron energy level

A specific amount of potential energy that an electron can possess

Electron shell

An energy level associated with an electron's average distance from the nucleus

First electron shell

The shell closest to the nucleus and the lowest in potential energy

Maximum electrons in the first shell

2 electrons

Maximum electrons in the second shell

8 electrons

What happens when an electron absorbs energy?

It moves to a shell farther from the nucleus

What happens when an electron loses energy?

It moves to a shell closer to the nucleus and releases energy

Chemical behavior of an atom

Determined by the distribution of its electrons, especially those in its outermost shell

Valence electrons

Electrons in an atom's outermost electron shell

Valence shell

The outermost electron shell of an atom

Completed valence shell

A full outer electron shell that generally makes an atom chemically unreactive

Inert

Chemically unreactive because of a completed valence shell

Orbital

The three

Maximum electrons per orbital

2 electrons

1s orbital

The single spherical orbital in the first electron shell

Second electron shell orbitals

One 2s orbital and three 2p orbitals

2s orbital

A spherical orbital in the second electron shell

2p orbitals

Three dumbbell

Maximum electrons in the four second

shell orbitals

Unpaired electrons

Electrons in valence

Chemical bond

An attraction that holds atoms together

Chemical bonding

The process by which atoms interact through their valence electrons and are held together

Molecule

Two or more atoms held together by covalent bonds

Covalent bond

A bond formed when two atoms share a pair of valence electrons

Single bond

A covalent bond involving one shared pair of electrons

Double bond

A covalent bond involving two shared pairs of electrons

Molecular formula

A formula showing the types and numbers of atoms in a molecule

Structural formula

A representation showing how atoms are connected by bonds

Lewis dot structure

A representation using dots around element symbols to show valence electrons

Space

filling model

Ball

and

Valence

The bonding capacity of an atom

Valence of hydrogen

1

Valence of oxygen

2

Valence of nitrogen

3

Valence of carbon

4

Why can oxygen usually form two bonds?

Oxygen has 6 valence electrons and needs 2 additional electrons to complete its valence shell

Electronegativity

An atom's attraction for the shared electrons in a covalent bond

Nonpolar covalent bond

A covalent bond in which electrons are shared equally between atoms

Polar covalent bond

A covalent bond in which electrons are shared unequally between atoms

Why are O

H bonds polar?

Partial negative charge

A slight negative charge on an atom that attracts shared electrons more strongly

Partial positive charge

A slight positive charge on an atom whose shared electrons are pulled toward another atom

Ion

An atom or molecule with a net electrical charge

Cation

A positively charged ion

Anion

A negatively charged ion

How does a cation form?

An atom loses one or more electrons

How does an anion form?

An atom gains one or more electrons