FITE Notes: Chemistry

Chemistry is the study of matter, which is anything that has mass and takes up space. Everything around you is matter, and it shows up in different states.

States of Matter

• ●Solid: fixed shape and fixed volume. Particles packed tight.
• ●Liquid: takes the shape of its container but keeps a fixed volume. Particles slide past each other.
• ●Gas: fills its whole container. Particles are spread far apart and move fast.

Physical vs Chemical Changes

• ●Physical change: the substance changes form but stays the same substance. Melting ice, ripping paper, dissolving sugar.
• ●Chemical change: a new substance forms. Burning wood, rusting iron, baking a cake. Signs include color change, gas bubbles, heat, or light.

SI Units and Significant Figures

• ●Length is measured in meters (m), mass in kilograms (kg) or grams (g), and time in seconds (s).
• ●Volume is often measured in liters (L), and temperature in Kelvin (K) or Celsius (C).
• ●Significant figures are the digits in a measurement you actually know for sure, plus one estimated digit. They tell you how precise a measurement is.

An atom is the smallest unit of an element. It is built from three particles, and where they sit matters.

• ●Protons: positive charge, found in the nucleus (the center).
• ●Neutrons: no charge (neutral), also in the nucleus.
• ●Electrons: negative charge, zooming around the nucleus in the electron cloud.

Atomic Number and Mass Number

• ●Atomic number = the number of protons. This is what makes an element that element. Every carbon atom has 6 protons.
• ●Mass number = the number of protons plus the number of neutrons.
• ●In a neutral atom, the number of electrons equals the number of protons.

Isotopes

Isotopes are atoms of the same element that have different numbers of neutrons. They have the same atomic number but a different mass number. Carbon-12 and carbon-14 are both carbon, but carbon-14 has two extra neutrons.

The periodic table is a map of all the elements, organized by atomic number (number of protons). It is set up so elements with similar behavior line up together.

Groups vs Periods

• ●Groups (also called families) are the vertical columns. Elements in the same group act alike because they have the same number of outer electrons.
• ●Periods are the horizontal rows. As you move across a period, the atomic number goes up by one each step.

Big Regions

• ●Metals: on the left and middle. Shiny, conduct electricity, bendable.
• ●Nonmetals: on the upper right. Often dull and poor conductors.
• ●Noble gases: far right column. Very stable and barely react.

Periodic Trends (Plain Terms)

• ●Atomic size: atoms get bigger going down a group and smaller going across a period to the right.
• ●Reactivity: metals on the far left are very reactive; noble gases on the far right are not.

Atoms bond to become more stable. Most atoms want a full outer shell of electrons, and bonding is how they get there.

Ionic Bonds

• ●One atom gives up electrons and another takes them.
• ●This usually happens between a metal and a nonmetal.
• ●The atoms become charged ions and stick together by opposite-charge attraction. Example: NaCl, table salt.

Covalent Bonds

• ●Atoms share electrons instead of giving them away.
• ●This usually happens between two nonmetals.
• ●Example: H2O, water, where oxygen shares electrons with two hydrogens.

In a chemical reaction, starting substances change into new substances. The reactants are what you start with (on the left), and the products are what you make (on the right). An arrow points from reactants to products.

Main Reaction Types

• ●Synthesis: two or more things combine into one. A plus B makes AB.
• ●Decomposition: one thing breaks into smaller pieces. AB makes A plus B.
• ●Single replacement: one element trades places with another in a compound.
• ●Double replacement: two compounds swap partners.
• ●Combustion: a fuel reacts with oxygen, releasing energy as heat and light.

Why You Balance

The law of conservation of mass says matter is not created or destroyed. So you must have the same number of each kind of atom on both sides of the equation. You balance by adding numbers called coefficients in front of formulas. Never change the little subscript numbers inside a formula.

1. 1Count how many of each atom you have on each side.
2. 2Add a coefficient in front of a formula to fix whichever atom is unbalanced.
3. 3Recount and adjust until every atom matches on both sides.
4. 4Check that your coefficients are the smallest whole numbers possible.

Atoms are way too small to count one at a time, so chemists count them in big groups called moles, the same way you count eggs in dozens.

Molar Mass

The molar mass of a substance is the mass of one mole of it, measured in grams. You find it by adding up the atomic masses from the periodic table. It lets you switch between grams and moles.

Mole Ratios (Kept Simple)

• ●A balanced equation tells you the ratio of moles between substances. The coefficients are the ratio.
• ●If an equation shows 2 H2 plus 1 O2 makes 2 H2O, then 2 moles of hydrogen react with 1 mole of oxygen.
• ●Stoichiometry just means using those mole ratios to figure out how much product you get or how much reactant you need.

The kinetic theory says all matter is made of tiny particles that are always moving. The hotter something is, the faster its particles move. This idea explains why solids, liquids, and gases behave the way they do.

How Gases Behave

• ●Gas particles move fast, spread out, and bounce off the walls of their container.
• ●Pressure is caused by gas particles hitting the walls of the container.
• ●Three things describe a gas: pressure, volume, and temperature. Change one and the others respond.

Boyle's Law

At a constant temperature, pressure and volume are inverses. Squeeze a gas into a smaller volume and the pressure goes up. Give it more room and the pressure drops.

Charles's Law

At a constant pressure, volume and temperature rise together. Heat a gas and it expands; cool it down and it shrinks. Temperature must be measured in Kelvin for these laws.

Acids and bases are two opposite groups of substances. You measure how acidic or basic something is with the pH scale.

Properties of Acids

• ●Taste sour (lemons, vinegar). Never taste lab chemicals.
• ●Release hydrogen ions (H+) in water.
• ●React with many metals and turn blue litmus paper red.

Properties of Bases

• ●Taste bitter and feel slippery (soap, baking soda).
• ●Release hydroxide ions (OH-) in water.
• ●Turn red litmus paper blue.

Neutralization

When an acid and a base react, they cancel each other out and produce water and a salt. This is called neutralization. For example, an acid plus a base can make water (H2O) and a salt such as NaCl.