6.1: Atoms, Elements, and Compounds Chemistry is the study of matter. Matter is anything that has mass and takes up space. Atoms are the building blocks of matter. THE STRUCTURE OF ATOMS: Billions of atoms could fit on the head of a pin! Atoms are made up of even smaller particles – Neutrons Protons Electrons

The Structure of Atoms: Nucleus – the center of an atom Within this nucleus are protons and neutrons. Neutrons – particles that have no charge Protons – particles with a positive charge Electrons – negatively charged particles located outside the nucleus. Constantly move around the nucleus in energy levels. Are attracted to the protons Atoms contain an equal number of protons and neutrons so the overall charge of an atom is neutral.

An Atom:

Elements:

An element is a pure substance that cannot be broken down into other substances by chemical or physical means. Are made of only one type of atom. Information collected about each element has been organized into a chart called the periodic table of elements. Organized into horizontal rows called periods, And vertical columns called groups.

Carbon: Is an extremely important element in biology and chemistry because nearly all of the molecules of living things contain carbon.

Isotopes: Isotopes – atoms of the same element that have different numbers of neutrons. Mass number (A) = number of protons and neutrons. Atomic number (Z)= number of protons in the nucleus. How many neutrons in Carbon 14? Neutrons have no charge so a change In their number has no effect on charge. Carbon 14 is a radioactive isotope.

Radioactive Isotopes: A change in the number of neutrons CAN change the stability of the nucleus causing it to decay (or break apart). When a nucleus decays, it gives off radiation that can be detected and used for many applications. Isotopes that give off radiation are called radioactive isotopes. Carbon 14 is a radioactive isotope found in all living things. Half life – the amount of time it takes for half of the carbon 14 to decay.

Compounds Elements can combine to form more complex substances. Compounds are pure substances formed when two or more different elements combine. NaCl CaCl H2O CO2

6.2: Chemical Reactions Chemical reactions allow living things to grow, develop, reproduce, and adapt. The human body is a 24 hour reaction factory! A chemical reaction is the process by which atoms or groups of atoms in substances are reorganized into different substances. Chemical bonds are broken and/or formed during chemical reactions.

Rust forms when oxygen in the air reacts with iron:

A light stick consists of a glass vial, containing one chemical solution, housed inside a larger plastic vial, containing another solution. When you bend the plastic vial, the glass vial breaks, the two solutions flow together, and the resulting chemical reaction causes a fluorescent dye to emit light.

Physical Changes It’s important to know that substances can undergo changes that do not involve chemical reactions. Water, for example, can undergo physical changes:

Reactants and Products A chemical equation shows the reactants on the right side of an arrow, and the products on the left. Reactants – the starting substances of a chemical reaction. Products – The substances formed during the reaction. Reactants Products C 6 H12O 6 + O2 6CO2 + 6H2O Glucose and oxygen react to form carbon dioxide and water. (This is cellular respiration.) In chemical reactions, matter cannot be created not destroyed. All chemical equations must show a balance of mass.

Section 6.3: Water and Solutions Properties of water (H2O): Water is a polar molecule – it has an unequal distribution of charges. Hydrogen bonds – a weak attraction involving a hydrogen atom and an oxygen atom. This is a van der Waals force which is responsible for keeping water molecules together. Water has surface tension due to van der Waals forces. Water striders can stand on water. Water droplets can form.

Mixtures A mixture is a combination of two or more substances in which each substance retains its individual characteristics and properties. Homogenous mixture – uniform composition throughout Heterogenous mixture – components remain distinct, do not dissolve A solution is a homogenous mixture. Two components of a solution are: Solvent – substance in which another substance is dissolved Solute – the substance that is dissolved in the solvent.

Acids and Bases: Acids are substances that release hydrogen ions when dissolved in water. The more hydrogen ions a substance releases, the more acidic the solution becomes. Substances that release hydroxide ions (OH-) when dissolved in water are called bases. NaOH is a common base that breaks apart in water to release Na+ and OH- ions. The more OH- ions present, the more basic a solution is.

pH: The amount of hydrogen ions or hydroxide ions in a solution determines the strength of an acid or a base. We can easily measure the pH of a solution using a pH meter or pH paper. See the pH scale to the right. Water is neutral (pH 7) Acids have a pH lower than that of water. Bases have a pH higher than that of water. What’s a buffer?

Photosynthesis Equation: 6CO 2 6H 2 O Solar energy C 6 H 12 O 6 6O 2 WARM-UP: 1. List the atoms involved in photosynthesis. 2. List the molecules involved in photosynthesis. 3. List the compounds involved in photosynthesis.

Chemical Equation for Cellular Respiration: 6CO 2 6H 2 O energ y C 6 H 12 O 6 6O 2 Cellular Respiration: Carbohydrates + oxygen = carbon dioxide + water + energy