Chemistry

The Atom and the Periodic Table

A Picture of an Atom• Most of an atom is empty

space!• The nucleus contains most

of the mass of the atom• The # of protons = the # of

electrons (in a neutral atom)• The # of protons determines

which element the atom is• The number of neutrons can

change – this is called an isotope

• Some elements can lose an electron(s) (become positively charged) or gain an electron(s) (become negatively charged) – charged atoms are called ions

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Mass

Atomic Mass = # of protons + average # of neutrons

Period

Family or Group

# of valence electrons

Electrons are placed in specific electron shells. Each period number equals the number of electron shells in the atom, which stays the same for all the elements in each period

Elements in a group or family have similar properties (characteristics) and undergo the same type of chemical reactions (due to having the same number of valance electrons)

Elements across a period change in a regular way (the # of protons increases as does the #of electrons and the atomic mass), but the number of electron shells stays the same

Properties of Matter

All Pure Matter has Physical Characteristics

• Can observe without changing into a new substance

• Examples: boiling point, freezing/melting point, hardness, color, texture, & state at room temperature (gas, liquid or solid), density, solubility (if possible) in water or non-polar solvent

• If a metal: luster, malleability, conductivity of electricity and heat, attraction to magnet

If matter undergoes a physical change, then it is the same substance with the same physical and chemical properties

• Example: an ice cube, liquid from the faucet, and steam from a boiling pot are all water.

• Each state has the same chemical formula, freezing/melting and boiling points, clear color, and is the universal solvent.

All Pure Matter has Chemical Characteristics

• Can’t be observed just by looking at it• Describes ability to turn into a new substance• To observe the property, the substance MUST

react with another and form other pure substance(s), SO there must be a chemical reaction

• Examples: flammability, reacts with gas (iron to form rust, copper turns green, silver tarnishes), reacts with metals (acids)

If matter undergoes a chemical reaction,

there is a new substance with its own

physical & chemical properties

• Sodium (Na) - soft, silvery metal that explodes in water

• Chlorine (Cl) - a poisonous yellow-green gas.

Chemical Reaction:sodium chloride (NaCl)

•a white solid•dissolves in water without exploding•safe to eat – table salt•melting point of 801°C (Na 97.85°C)•boiling point of 1413°C (Cl -34.6°C).

Mixtures

Compounds vs. Mixtures

• A compound is a pure substance made of 2 or more atoms (molecule) that reacted chemically and has unique chemical properties of its own.

• A mixture is made of 2 or more substances that do no react chemically, and retain their chemical properties.

Types of Mixtures

• Heterogeneous – no matter how well mixed, you can still see the separate parts

• Example – salad: lettuce, tomatoes, croutons, etc.; can pick out the cucumber slices if you don’t like

• Homogeneous – parts are so evenly mixed, you can’t see the different parts; looks like one substance

• Example – teaspoon of sugar stirred into hot tea; can’t see sugar but the tea tastes sweet.

What is another name forhomogeneous mixture?

• Solution – a well-mixed mixture• At least one substance dissolves into another• Solute – substance dissolved into the 2nd

substance (smaller amount)• Solvent – substance that surrounds the 1st

substance (larger amount)• Solubility is a measure of how much solute

goes into solvent at a given temperature – this is a physical property

Are all solutions a solid dissolving into a liquid?

• Liquid into liquid

• Gas into gas• Gas into liquid

• Solid into solid

• Anti-freeze: ethylene glycol into water

• Oxygen in air• Oxygen in water, CO2 in

soda water• Alloys: metal in metal

such as bronze (Sn in Cu), brass (Zn in Cu), 14 kt gold (Ag, Cu, or Zn in Au)

Factors That Affect Solubility

•Temperature•Pressure•Solvent compatibility

Temperature Affects Solubility

• ↑ solid’s solubility by ↑ temperature, genetallygenerally

• ↑ gas’ solubility by ↓ temperature

Pressure Affects Solubility

• ↑ gas’ solubility by ↑ pressure over the solvent

Solvent Compatibility - Like Dissolves Like

• Polar solvent + ionic compound

• Water is a polar molecule: (+) & (-) sides

• Salt is an ionic compound• The sodium ion (Na+) is

attracted to water’s (-) side

• The chlorine ion (Cl-) is attracted to water’s (+) side.

Polar Solvent + Polar Solute

• Polar ammonia molecules dissolve in polar water molecules.

• The +H of the water molecule is attracted to the –N of the ammonia molecule AND…

• The +H of the ammonia molecule is attracted to the –O of the water molecule

Non-polar + non-polar• Even if a substance is soluble, it may not dissolve in water• Non-polar: no (+) & (-) parts of molecule• Acetone is a solvent that is partially polar• The components in nail polish are non-polar chemicals (resins) dissolved in acetone• Letting your nails dry means allowing the solvent

to evaporate leaving the resin behind.• To remove, the polish needs to dissolve• This is the same reason you can’t clean oil-based

paint from a paint brush using water. You must use turpentine.

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Describing Acids and Bases

Chemical Properties of Acids

• Tastes sour (if in food)• Reacts with metals and carbonates• Turns blue litmus paper red• pH < 7• Separate into H+ and (-) ions in water

Never Taste a Chemical in a Lab

• Acids in foods taste sour or tart: citrus fruits, tomatoes, apples, vinegar

Acids React with Metals & Carbonates

• Acids corrode metals• H+ react with the metal• Chemical reaction

producing H2 – gas

• Acids react with carbonates to produce CO2

Strong Acid versus Weak Acid

A strong acid releases more H+ into solution. A weak acid only partially dissolves in water

Chemical Properties of Bases

• Tastes bitter (if in food)

• Feels slippery• Turns red litmus paper blue• pH > 7• Causes OH- and (+) ions in water

Sodium Hydroxide - NaOHPotassium Hydroxide - KOHAmmonium Hydroxide - NH4OHCalcium Hydroxide - Ca(OH)2

Magnesium Hydroxide - Mg(OH)2

Barium Hydroxide - Ba(OH)2

Aluminum Hydroxide - Al(OH)3

• Bases in food taste bitter: radish, cabbage, Brussels sprouts, turnip, olives, coffee, unsweetened cocoa, quinine, Tums®

• Indicator paper call tell you if a substance is acid (< 7), base (> 7) or neutral (= 7)• The closer to 0, the stronger the acid• The closer to 14, the stronger the base (or more alkaline)• The closer to 7, the weaker the acid or base• Strength determines safety

What Happens If An Acid & Base Mix?

• Neutralization = reaction between acid and base

• Resulting substance is less acidic, less basic than the original substances

• acid + base = a salt + water

• How close to pH 7 depends on the concentrations and amounts of the originals