Everything in the universe is composed of ATOMS, the basic building blocks of matter How small is an atom? The thickness of a piece of paper is about 1 million atoms. CHALLENGE: What does an atom look like? Draw a picture of an atom to the best of your ability.

YES we can! It has only been in the last 2 decades that we can see them, using the most powerful electron microscopes in the world. These are carbon atoms (within a sheet of graphite)

Over the past 200 years, scientists have conducted many experiments that provide evidence of an atom’s properties. We have developed several atomic models based on this. ORBITAL MODEL BOHR MODEL ELECTRON CLOUD MODEL

An atom is composed of two regions: 1.NUCLEUS -Contains PROTONS (+) and NEUTRONS (0), which are held together by the “strong force” 2.ELECTRON CLOUD -Where the electrons (-) are found; but we don’t know exactly where they are because they’re “zipping” around constantly at the speed of light

Electron cloud (negatively charged) Nucleus (positively charged)

An atom has an overall charge of zero (neutral), because it has an equal number of protons & electrons But an atom doesn’t always stay neutral. Electrons can be lost or gained between atoms, resulting in: IONS, which are charged particles, such as Na + or Cl -

The identity of an atom is determined by the number of protons The Periodic Table is arranged by the number of protons in each element. # of protons = ATOMIC NUMBER

The Periodic Table of Elements

Elements are pure substances that can’t be broken apart by chemical means and are composed of identical atoms. There are more than 100 elements The first 92 are found in nature, but the rest are man-made (particle physics) Some elements are unstable and radioactive Example: Uranium

Two or more elements can bond together to form molecules and compounds Examples of molecules & compounds: –WaterH 2 0 –Carbon DioxideCO 2 –Oxygen GasO 2 –GlucoseC 6 H 12 O 6 –Sodium ChlorideNaCl –LimestoneCaCO 3 –PropaneC 3 H 8

There are three basic types of bonds: 1.IONIC BOND: Electrons are transferred from metals to nonmetals  metal ions lose electrons, and nonmetal ions gain electrons  This type of bond is very strong and results in solid crystal structures, such as NaCl (table salt)

2. COVALENT BOND: Electrons are shared between two or more nonmetals  This type of bond is weaker than ionic bonds and results in compounds that are gases or liquids, such as H 2 O and CO 2

3. HYDROGEN BOND: Occurs between water molecules, because water is POLAR which means that a part of the molecule is positively charged, while another part is negatively charged NONPOLAR molecules have no charge

When water molecules are next to each other, they line up in a certain way because the Hydrogens (+) are attracted to the Oxygens (-), which creates hydrogen bonds

Water is one of the most unique molecules known to man and also one of the most important to living organisms. Not only does water exist in nature in all three states of matter (solid, liquid, gas), it also covers 75% of the earth and makes up approximately 78% of the human body. Water has special properties, due to the hydrogen bonding between its molecules.

Cohesion is an attractive force between particles of the same kind Cohesion between water molecules creates surface tension on the top layer of the water, causing it to behave as an elastic sheet. Example: water bugs are able to “walk on water” because they are light and have long legs to distribute their weight along the surface tension.

Adhesion is the attraction between molecules of two different substances Water molecules will form hydrogen bonds with many other materials (such as glass, soil, plant stems, paper) This results in capillary action, where water molecules move through a substance quickly, or “climb” up a thin tube against gravity

A split celery stalk is placed into two different cups of water with food coloring. Water molecules can move upwards against gravity, through thin tubes of xylem tissue in the stem. This is how plants are able to transport water from their roots up to their leaves. Example of capillary action:

Water is called the “Universal Solvent” because of its polar nature; it can dissolve many other polar substances “Like dissolves Like” Pure water cannot dissolve nonpolar substances, such as: –Oils and fats –Plastic, Gasoline –Sand & Glass –Certain metals, like pure Gold & Silver

Water cannot dissolve… Olive oil Gasoline

Water is very resistant to changes in temperature; it takes a lot of energy to heat up or cool down Specific heat: How much heat energy is required to raise the temperature of 1 gram of a substance by 1°C Example: When you place a pot of water on the stove, the average time for it to begin to boil is 5 to 10 minutes – that’s a long time!

Water is an essential substance in all living things because of its ability to: 1. Resist temperature changes 2. Move through materials quickly 3. Dissolve many substances These properties allow an organism to maintain homeostasis, which is the cell’s stable internal environment

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SOLUTION: a homogeneous mixture in which the particles are very small and well-mixed Example: salt water SOLUTE: the substance being dissolved Example: salt SOLVENT: the substance doing the dissolving Example: water

ACIDS: produce H+ ions in water –Acids taste sour –Acids are corrosive to metal –pH lower than 7 Examples: LEMON JUICE VINEGAR HYDROCHLORIC ACID

BASES: produce OH - ions in water –Bases taste bitter –Bases are slippery –Also called “alkaline” –pH higher than 7 Examples: AMMONIA BAKING SODA LYE (in soaps) BLEACH

INDICATOR: a chemical that changes color in the presence of an acid or a base –pH paper: Turns a range of colors, must compare to the color chart to determine pH –Litmus paper: Turns red = acid Turns blue = base –Phenophthalein: turns pink in a base –Natural indicators: red cabbage juice –Electronic pH meters: very precise

Controlling the pH level in living cells is very important in maintaining homeostasis Most cells function only within a very narrow pH range Example: blood pH is 6.8 – 7.8 Control of pH is accomplished with buffers made by the body