Chapter 2

Introduction to “Baby Chemistry”

Life depends on chemistry

We need to be able to understand the chemistry before we move on to understand the rest of body

Atom - the basic unit of matter

Atoms are made of 3 subatomic particles

1. Protons - positive charge2. Neutrons – neutral charge3. Electrons – negative charge

Protons and neutrons are found in the atoms nucleus - The center of the atom

Electrons are found outside the nucleusElectron cloudThey are in constant motionAre attracted to positive charge of nucleus

but remain outside due to energy of motion

What is the overall charge of the nucleus?

What is the overall charge of the electron cloud?

Nucleus (+) & Electron Cloud (-)Therefore, atoms are

neutral from equal numbers of protons and electrons

Elements – pure substances that consist of entirely 1 type of atom

They are represented by 1, 2 or 3 letters

There are 117 elements (periodic table in back of book)

Based on certain characteristics of

each element

Periodic table includes information on atomic mass and atomic number

Atomic Number – number of protons (and therefore electrons)

Atomic Mass – sum of protons and neutrons

How are isotopes different?

Q) How are isotopes different?

R) They have a different number of neutrons

Isotopes are identified by their atomic mass number (protons + neutrons)

All isotopes still have the same chemical properties (because neutrons are neutral)

Have nuclei that are unstable and break down at constant rates over time

Important Uses1.Determine age of rocks2.Treat cancer and kill bacteria that cause

food to spoil3.Used as “tracers” to follow substances

in the body

*In nature, most elements are found combined with other elements in compounds

• Compound – substances formed by the chemical combination of 2 or more elements

What information is contained in a chemical formula?

1. Type of atoms2. How many of those atoms

Example) Q) What’s in H20?

A) 2 hydrogen and 1 oxygen

Physical and chemical properties of a compound are usually different from those of elements from which they are formed

Example – NaClSodium Chloride : Table SaltSodium (Na) – silver colored metalChlorine (Cl) – greenish gas

+ =

Hold compounds together

Involves the outer electrons (valence electrons) that surround each atom’s nucleus

3 types of bonds1. Ionic (strongest)2. Covalent3. Van Der Waals Forces (weakest)

One or more electron is “transferred” from one atom to another

An atom that loses an electron has a positive charge

An atom that gains an electron has a negative charge

Positively or negatively charged atoms are called ions

When electrons are “shared” instead of being “transferred”

How do they share electrons?The electron travels in the orbits of both

atoms

Single bond – 2 electrons shared Double bond – 4 electrons shared Triple bond – 6 electrons shared

Atoms joined by covalent bonds are called molecules

Water Molecule

Atoms in covalent bond don’t always share equally

Rapid movement of electrons creates “+” and “-” charges

When molecules are close together, an attraction can occur between oppositely charges regionCreates intermolecular “Vander Waals

Forces”

How does the gecko’s foot function similarly to Van Der Waals Forces?

The water molecule – H2O (think mickey mouse)

Water is a polar molecule

What is polarity?The uneven distribution of electrons which

causes the molecule to have regions with a positive and negative charge

Allows water to attract to other molecules

Most abundant compound in living things

Naturally occurring and found at any temperature on the earth

Water expands when it freezes, SO WHAT??How does that affect us?

Held together by hydrogen bonds (not as strong as ionic or covalent) which form between the hydrogen and oxygen

Why would this be important?

How many bonds are there per water molecule?

Allows 4 bonds to form

This bonding pattern is what makes water responsible for it’s many special properties

CohesionAn attraction between water molecules

Why can a spider walk on waterHow does water come out of a faucet?

AdhesionAn attraction of water to other molecules

How does a tree get water from its roots to its leaves?

Why does the water level in a graduated cylinder look curved?

Mixture – a material composed of 2 or more elements or compounds that are physically combined, but not chemically combined

Examples: Chocolate Chip Cookie Earths Atmosphere

2 types of Mixtures1.Solution2.Suspension

Is a mixture of 2 or more substances in which the molecules are evenly distributed

Example:Salt dissolving in water (the NaCl and H2O combine by the Cl- being

attracted to the H and the Na+ being attracted to the O)

2 important terms to knowSolute – substance being dissolvedSolvent – substance doing the dissolving

Q) Why is water considered the greatest solvent in the world?

A) Polarity allows it to pull other molecules apart

Mixture of water and non-dissolved material

Concentrations for hydrogen (H +) and hydroxide (OH-) ions are important indicators of the properties of a solution

A measurement system was created to indicate the concentration of the H + ions in the solution called the pH scalepH – potential of hydrogen

A pH of 7 = equal number of H + and OH- ions

A pH of 7 = equal number of H + and OH- ions

H + + OH- = H2O

Solutions with a pH < 7 are called acidsBecause more hydrogen ions (H +)

The lower the pH, the greater the acidity

Solutions with a pH > 7 are called alkaline or basicBecause more hydroxide (OH-) ions

The higher the pH, the more basic the solution

Each step of the pH scale represents a factor of 10

Ex) pH of 4 has 10x as many H + ions as a solution with a pH of 5

Acids BasesI-------------------------I-------------------------I

1 H + > OH- 7 H + < OH- 14H + = OH-

Weak acids or bases that can react with strong acids or bases to prevent sharp, sudden changes in pH

Why are buffers important?The pH of fluids within most cells of the

human body must generally be kept between 6.5 and 7.5

If pH is higher/lower – it will affect the chemical reactions that take place

Controlling the pH of cells is important for maintaining homeostasis