Chemistry

Basic ChemistryMatter, Energy, and

Organization

Chemistry

Composition of Matter

Energy

Solutions

Composition of Matter - Elements

Everything in the universe is made of matter and energy.

Matter is anything that has mass and volume. Living things are made of the same matter that makes up the nonliving world.

Mass is how heavy the matter is. Mass is measured with a balance. The standard SI unit used to measure mass is the kilogram.

Volume is how much space a substance occupies. The SI unit usually used to measure volume is the liter.

Elements are made substances made of only kind of atom. There are 92 naturally occurring elements in the universe.

The names of elements are abbreviated using chemical symbols composed of either one or two letters. The first letter is always capitalized and the second letter, if present, is never capitalized. Common symbols for the elements that make up living things are C, N, H, O, S, Na, Ca, K, and P.

Atoms – Part 1

The nucleus is composed of two tightly packed particles: a positively charged proton and a neutrally charged neutron. Almost all of the atom’s mass is in its nucleus.

The electron cloud is composed of only negatively charged electrons, which are high-energy particles with almost no mass. They orbit the atom’s nucleus at high speed at certain distances from the nucleus called energy levels.

The smallest part of an element that still has all of the properties of that element is an atom. Atoms are too small to be seen with any microscope, but scientists have been able to make models of their structure based on their behavior.Atoms have two parts: the nucleus and the electron cloud.

proton neutron

Nucleus

electron

Electron cloud (in energy levels)

Nucleus

Atoms – Part 2

All atoms an element have the same number of protons. This is the same as the atom’s atomic number.

In a neutral atom, the number of protons is the same as the number of electrons.

The mass number of the atom is the sum of the protons and neutrons in the atom.

Electrons in outermost energy levels have more energy than those in energy levels close to the nucleus.

The Periodic Table gives scientists information about the atomic structure of the elements.

Scientists can determine the number of protons, electrons, and neutrons using the atomic number and the mass number.

Fluorine: At. # = 9, Mass # = 19

protons = 9 electrons = 9

neutrons = (19 – 9) = 10

Compounds

An atom is stable when its outer energy level is full of electrons. The only reason that atoms react with each other is to get a full outer shell of electrons.

Atoms bond with other atoms in chemical reactions, combining so that they become more stable.

There are several types of chemical bonds that are important to living things. They are:

1) Ionic Bonds – one atom loses electrons and the other atom gains electrons

2) Covalent Bonds – atoms share electrons

3) Hydrogen Bonds – weak temporary attractions between polar covalent molecules

Most elements don’t exist by themselves. They form compounds when their atoms are joined together by chemical bonds. In a compound, the type and number of atoms are always the same. This is shown in the compound’s chemical formula, such as H2O, NaCl, and CO2, C6H12O6.

Ionic Bonding A Sodium atom (Na) has 11 electrons with only one electron in its

outer energy level. A Chlorine atom (Cl) has 17 electrons, with seven in its outer shell. Atoms are most stable with a full outer shell, which is usually 8 electrons.

In an ionic bond, the Na atom loses one electron to Cl. The Na atom now has a full outer shell of 8 electrons, and so does the Cl atom. They are both stable.

The atoms are joined in an ionic bond because they are no longer neutral. The Na atom now has 11 protons and only 10 electrons, so it has a +1 charge. The Cl atom now has 17 protons and 18 electrons, so it has a -1 charge. Unlike charges attract, so they stick together and make the compound sodium chloride (NaCl).Na

atom

Cl atom

Na+1 ion

Cl-1 ion

NaCl

Covalent Bonding Covalent bonds are

another type of bond formed between atoms attempting to complete their outer shells.

Sometimes, neither atom can lose electrons. If this is the case, then the atoms will share pairs of electrons in order to get a full outer shell part of the time.

Covalent compounds like water result from this type of bonding.

H atoms

O atom

Electron pairs are shared

A water molecule is

formed.

Hydrogen Bonds Many times, when covalent bonds are formed, the shared

electrons are shared unequally. This is true about water molecules. The O atom’s nucleus has a much stronger (+) charge than the H atom’s nucleus.

The O nucleus holds the cloud of electrons more strongly than the H nucleus. Therefore, O part of the water molecule has a partial (-) charge and the H part of the molecule has a partial (+) charge. Water is a polar molecule.

These partial charges cause H2O molecules to stick together in weak hydrogen bonds. Other molecules also form hydrogen bonds.

H2O molecules

(-)(+)

(-)

(+)

(-)

(+)

Weak Hydrogen Bonds are formed between molecules

as (+) and (-) partial charges attract each other.

Energy and Living Things Energy is the ability to cause

change or to do work. Energy can exist in several

forms-- heat, light, sound, chemical, mechanical, and electrical.

The first law of thermodynamics says that energy cannot be created nor destroyed, but only changes its form.

Energy can be converted from one form to another, but each time there is a conversion, some heat is changed into an unusable form.

Biologists describe free energy as the energy that is available for work, in other words—the usable energy.

As energy flows through a living thing, it often changes form. The chemical energy from your food is converted into mechanical energy to move your muscles and heat energy, which radiates off of your body into the air.

States of Matter All of the atoms and

molecules that make up matter are constantly in motion. The speed at which these particles move determines whether the substance is solid, liquid, or gas.

Particles of a solid are tightly packed and vibrate in place. Particles of a liquid move around each other freely, although they are still closely packed. Particles of a gas are spaced widely apart and move quickly in straight lines.

Solid-particles are tightly packed and only have enough energy to vibrate in place.

Liquid-particles are tightly packed but have enough energy to move freely over each other.

Gas-particles are spread wide apart and have enough energy to move very fast in straight lines.

Energy and Chemical Reactions - 1 Living things carry out many

thousands of chemical reactions in order to stay alive. Chemical reactions can be described by chemical equations.

CO2 + H2O H2CO3

reactants products

If the reactants have more free energy than the products, the extra energy is released when they react, and the reaction is called exergonic.

If the reactants have less free energy than the products, the extra energy is absorbed when they react, and the reaction is called endergonic.

Energy and Chemical Reactions - 2 For most chemical reactions to begin, energy must be added to

the reactants. This is called activation energy. Certain substances can reduce the activation energy needed

for a reaction. These substances are called catalysts. Enzymes are substances that act as catalysts in living things. A single cell may contain thousands of enzymes, each one

catalyzing its own special chemical reaction..

Reactants

Products

Lowered Activation Energy

Reaction Progress (with enzyme)

Reactants

Reaction Progress (without enzyme)

Products

Activation Energy

Energy and Chemical Reactions - 3 In living things, energy is

transferred from one molecule to another by a series of chemical reactions.

The energy is transferred when high-energy electrons are passed from molecule to molecule.

These reactions are called reduction-oxidation reactions or redox reactions.

Redox reactions always occur in pairs.

In the chemical reaction below,

Na + Cl NaCl, the Na atom loses and electron and the Cl atom gains the electron. Atoms that lose electrons are said to have been oxidized and atoms that have gained electrons have been reduced.

Na Na+1 + e- (oxidation reaction)

Cl + e- Cl-1 (reduction reaction)

Solutions A solution is a homogeneous

mixture in which one or more substances are evenly distributed into another substance.

Solutions can be mixtures of solids, liquids, or gases. Air is a mixture of gases, Alloys like 14K gold are mixtures of solids, and wine is a mixture of liquids. Sea water is a mixture of solids in a liquid solvent.

Many substances can act as solvents. Water is an excellent solvent. An aqueous solution is one where water is the solvent. These are important to living things, because all of the chemical reactions of living things happen in aqueous solutions inside of organisms.

Solutions can be mixed in any proportion. Solutions that contain lots of solute are concentrated and solutions with little solute are dilute.

The solute is the substance that has been distributed into the other substance. It is broken up into individual atoms, molecules, or ions.

The solvent is the substance that breaks apart the other substance.

Acids and Bases In water molecules, because the

O atom has a partial (-) charge and the H atoms have a partial (+) charge, and Hydrogen bonds are formed between water molecules.

Because of these partial charges, the O atom or one water molecule can occasionally remove the H atom from another water molecule! This is called dissociation.

H2O H+1 + OH-1 (Hydroxide ion)

H+1 + H2O H3O+1 (Hydronium ion)

When water dissociates, equal numbers of hydroxide and hydronium ions are produced. Water is neutral.

Certain substances, when dissolved in water, supply extra hydrogen ions or extra hydroxide ions.

Substances that supply extra hydrogen (hydronium) ions are called acids.

Substances that supply extra hydroxide ions are called bases.

The pH scale goes from 0 to 14 and tells whether something is acidic, basic, or neutral.

The pH Scale

0 7.0 14.0

Strong Weak

Acid Acid

Weak Strong

Base Base

neutral

Solutions and Living Things Cells are mostly water, so

whether something will dissolve in water is important to living things.

The pH of the cell is important too because enzymes work best within a narrow pH range.

Cells use buffers to control pH. A buffer is a chemical that can neutralize a small amount of an acid or a base.