8th Grade Chemistry

Chemistry Atoms/Atomic Structure: Atoms are the basic building blocks of all matter. Everything in the universe is made out of atoms. They are extremely small and are made of three particles; electrons, protons, and neutrons. Each of these particles makes up an atom, and multiple atoms make up matter. ❖ Protons: the positively charged part of an atom, located in the atom’s nucleus ➢ the atomic number of an element shows the number of protons within one atom of that element ■ EX: Beryllium, atomic number 4, has four protons in an atom. ❖ Neutrons: have no charge (neutrally charged), located in the atom’s nucleus ❖ Electrons: the negatively charged part of an atom, located in the electron cloud ➢ they have no fixed position, they are always moving ➢ Electron Cloud: The first energy level or ring can hold a maximum of two electrons. The second energy level or ring can hold a maximum of eight electrons. The third ring can hold a maximum of eighteen electrons. ■ Valence Electrons: electrons found in the outermost energy level The nucleus of an atom: The center of an atom where protons and neutrons are found. The mass number of an atom is the atomic mass of an element rounded up. Atomic Number: equal to the number of protons or the number of electrons (when the atom is neutral) Atomic Mass or Mass Number: equal to the number of protons plus neutrons Ion: An electrically charged atom (due to less/more electrons than proton ratio) Counting Atoms: A compound is two or more different elements that are chemically joined together. Each compound has its formula for the way of identifying it. In a compound, there are coefficients and subscripts. ❖ Coefficients are the big numbers in a chemical formula that are before the letter of the element. This number tells us how many molecules of the element there are in that compound. ❖ Subscripts are the numbers that follow an element and are usually lower than the letter. This represents how many atoms of an element are in a compound. Chemical Reactions: Indicators of a chemical change: ❖ Production of an odor ❖ Change in temperature, color, or pH ❖ Formation of gas or new substance The law of conservation of mass states that matter cannot be created nor destroyed. Chemical reactions must be balanced. The number of atoms in the reactant and product must be the same for the chemical reaction to be balanced. In every chemical reaction, there is a reactant and a product. ❖ The reactant is what the chemical reaction starts with. ❖ The product of a chemical reaction is what comes out of the chemical reaction. EX: CH4+2O2 >> CO2 + 2H2O Image: https://commons.wikimedia.org/wiki/File:Methane-combustion.svg Reactants: 1 atom of carbon, 4 atoms of hydrogen, 4 atoms of oxygen. TOTAL: 9 atoms Products: 1 atom of carbon, 4 atoms of hydrogen, 4 atoms of oxygen. TOTAL: 9 atoms This is a balanced chemical equation as the numbers of atoms in the reactant and product are equal. Since it is a balanced equation, it follows the law of conservation of mass. Trends of the Periodic Table: Chemist Dmitri Mendeleev saw that the elements of the periodic table vary periodically and he noticed that they created a pattern. There are many ways that the periodic table is organized. When you look at a periodic table often you will see numbers at the top of each column. These numbers are used to group the elements within that row. There are eighteen total columns. The columns are also categorized by the number of electrons in their outer rings, which is why columns also have another set of numbers with letters. For example, the elements in columns (groups) 3-12 are all transition metals, and the elements in group 18 are called noble gases. The elements in group 1 (minus hydrogen) can be called alkali metals and group 2 elements are classified as alkaline earth metals. Group 17 elements are called halogens. Groups 1A (column 1) and Group 7A (column 17) are unstable and both highly reactive. Group 1A has one valence electron, and group 7A has seven valence electrons. To be classified as a stable element, the last ring of an element must be full. Both these groups are close to being full and either need electrons or need to give electrons making them highly reactive with other elements. Group 8A (column 18) is made up of noble gases which are all stable or inert. The outer shell of electrons is full of eight electrons and doesn’t need to gain or lose any electrons. Since the outer shell is full the elements are completely stable.