Biochemistry Unit Chapter 6 Section 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: LocationChargeNumber ProtonNucleusPositiveAtomic Number NeutronNucleusNeutralMass – (minus) Atomic number ElectronElectron CloudNegativeAtomic Number

 How many protons, electrons, and neutrons does each of the following elements have? ProtonsElectronsNeutrons 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 (H 2 O) because it is made of 2 hydrogen atoms and 1 oxygen atom.  Carbon Dioxide (CO 2 ) 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.