ESCS Review

Composition of Matter (Review) Matter – anything that takes up space, and has mass. Mass – the quantity of matter an object has. Element – substances that cannot be broken down chemically into simpler kinds of matter. Atom – the simplest part of an element that retains all the properties of that element. Nucleus – central region, and the bulk of the mass of an atom.

Composition of Matter (Review) Protons – positively charged subatomic particle, part of the nucleus. Neutron – subatomic particle with no charge, other part of the nucleus. Electron – negatively charged subatomic particle, found outside the nucleus. Atomic number – the number of protons an atom has. Mass number – number of protons + neutrons. Isotopes – atoms of the same element, that have a different number of neutrons.

Compounds (Review) Compounds – made up of atoms of two or more elements in fixed proportions. Chemical Bonds – the attractive forces that hold atoms together. Covalent Bond – forms when two atoms share one or more pairs of electrons. Ionic Bond – forms when electrons are transferred from one atom to another. The resulting positive and negative charged cause them to be attracted to each other (bonding). Ion – an atom or molecule with an electrical charge. Molecule – the simplest part of a substance that retains all the properties that make up its identity.

Energy (Review) Energy – the ability to do work. Chemical reaction – one or more substances change to produce one or more different substances. Energy is absorbed or released. Reactants – substances you start with in a reaction (left of the arrow). Products – substances you end up with after a reaction (right of the arrow). Activation energy – energy required to start a reaction.

Solutions (Review) Solution – mixture where one substance is uniformly distributed (dissolved) in another. Solute – the substance that is dissolved. Solvent – the substance in which the solute is dissolved. Concentration – the amount of solute in a solvent.

Water (Review) Polar compounds – have an uneven distribution of charge. Hydrogen bond – the force of attraction between a hydrogen molecule with a positive charge, and another molecule with a negative charge. (causes water to cling to itself).

Acids & Bases (Review) Acid – contains hydrogen (hydronium) ions. (H+) Found from 1-6 on the pH scale (1 being the most acidic, 6 being the least). Base – contains Hydroxide ions. (OH-) Found from 8-14 on the pH scale (14 being the most basic, 8 being the least). Neutral – equal amounts of (H+) and (OH-). Found at 7 on the pH scale. Buffers – chemical substances that neutralize small amounts of either an acid or a base.

Practice Questions 1. If an atom is made up of 6 protons, 7 neutrons, and 6 electrons, what is its atomic number? A. 6 B. 7 C. 13 D. 19

Practice Questions 2. The amount of energy needed for this chemical reaction to begin is shown by the line rising from the reactants. What is this energy called? A. chemical energy B. electrical energy C. activation energy D. mechanical energy

Practice Questions 3. What is an aqueous solution that contains more hydroxide ions than hydronium ions called? A. a gas B. a base C. a solid D. an acid

Practice Questions 4. The covalent bonds of a water molecule have partial positive charges on the hydrogen atom and a partial negative charge on the oxygen atom. What do the partial positive and partial negative charges on this water molecule mean? A. Water is an ion. B. Water is a polar molecule. C. Water needs a proton and two electrons to be stable. D. Oxygen atoms and hydrogen atoms have opposite charges.

Properties of water Cohesion is an attractive force that holds molecules of a single substance together, such as water molecules. Adhesion is the attractive force between two particles of different substances, such as water molecules and glass molecules. Capillary action – the attraction between molecules that results in the rise of the surface of a liquid when in contact with a solid.