Biochemistry UnitChapter 6Section 1

An element is a substance that can’t be broken down into simpler substances.

90 elements occur naturally on Earth.

25 elements are essential to the living things.

The 4 most important are Carbon, Hydrogen, Oxygen, and Nitrogen (CHON) which make up 96% of a human

Trace elements are elements that are needed by living things in small amounts: iron, iodine, fluorine...

Elements are arranged in a table called the “Periodic Table of the Elements”

Atomic Number=# protons# electrons

Neutrons =Atomic mass-Atomic Number:

11-5=6 Neutrons

An atom is the smallest particle of an element that still has the characteristics of that element.

The center of the atom is called the nucleus It is surrounded by an electron cloud.

There are 3 subatomic particles you need to know:

Location Charge Number

Proton Nucleus Positive Atomic Number

Neutron Nucleus Neutral Mass – (minus) Atomic number

Electron Electron Cloud Negative Atomic Number

How many protons, electrons, and neutrons does each of the following elements have?

Protons Electrons Neutrons

Carbon

Nitrogen

Gold

Electrons travel around the nucleus in energy levels.

The first level holds 2 electrons. The second level holds 8 electrons. The third level holds 18 electrons.

Atoms of the same element that have different numbers of neutrons are called isotopes.

Carbon-12 has an atomic mass of 12 and an atomic number of 6.

It has 6 protons, 6 electrons, and 6 neutrons.

Carbon-13 has one extra neutron, for a total of 7.

A compound is made of atoms of two or more elements combined.

Water is a compound (H2O) because it is made of 2 hydrogen atoms and 1 oxygen atom.

Carbon Dioxide (CO2) is made of one carbon atom and 2 oxygen atoms.

Covalent bonds form when 2 or more atoms SHARE electrons.

Ionic bonds form when atoms either gain or lose electrons.

A molecule is a group of atoms held together by covalent bonds, and has no overall charge.

An ion is a charged particle.◦ If an atom gains an electron, it becomes more

NEGATIVE◦ If an atom loses an electron, it becomes more

POSITIVE

A mixture is a combination of substances in which the individual components retain their own properties.

For example, if you mixed sand and sugar, you could still tell the individual grains apart.

A solution is a combination of substances in which the individual components combine and form a new, different substance.

For example, Kool-aid powder dissolves in water to make a tasty drink.

The pH is a measure of how acidic or basic a solution is.

pH can be from 0 to 14.

Acids are below 7 (lemon juice, tomatoes). They form H+ ions in water.

Bases are above 7 (ammonia, drain cleaner, eggs). They form OH- ions in water.

Water is neutral, and has a pH of 7.