CHEMICAL CHANGES WHAT IS A CHEMICAL CHANGE? • Chemical Change- produces substances that have new and different properties. • Signs: a change in color, heat or light is given off, gas is produced, or powdery solid settles out of a liquid. • The mass of the matter does not change. • Compound- a chemical combination of 2 or more substances. • A compound has its own properties, different from that of the substances it is made of. Rust is one example of a chemical reaction and a compound. WHAT ARE CHEMICAL BONDS? • Chemical Bonds- the links that atoms or electronically charged particles can form with one another. • They result from electrical attraction between atoms. • When atoms of different elements bond together, compounds are formed. • Chemical Formula- the ratio in which atoms are bonded together in a compound. • A way of using letters and numbers to show how much of an element is in a substance. • Example: Water is made of 2 hydrogen atoms and 1 oxygen, so its chemical formula is 퐻2푂. TYPES OF CHEMICAL BONDS • There are 2 types of chemical bonds: • Covalent Bonds • Ionic Bonds HOW DO COVALENT BONDS FORM? • Covalent Bond- formed when two nuclei attract the same electrons. • In a covalent bond, 2 atoms share electrons. • Usually the elements that form covalent bonds are: • Nonmetals: hydrogen, oxygen, carbon, and nitrogen. • May form between atoms of the same element or different elements. • When atoms are identical, they share electrons equally. • When the atoms are different, one atom attracts electrons more strongly than the other. HOW DO IONIC BONDS FORM? • Ionic Bond- when a metal atom transfers and electrons to a nonmetal atom. The charges of the ions are attracted to each other. • Ion- a particle with unequal numbers of protons and electrons. • Has an electric charge. • The sodium ion in the picture has a charge of +1 because it has one more proton than electrons. • The chloride ion in the picture has a charge of -1 because it has one more electron than protons. WHAT IS A CHEMICAL REACTION? WHAT ARE CHEMICAL REACTIONS? • Chemical Reactions- are chemical changes. • The original substances are called reactants. • The new substances produced by the chemical change are products. • 3 Main Types • Synthesis Reaction- involve 2 separate things joining together to form 1 compound. • Example- Steel Wool Rusting • Replacement Reaction- takes place when elements switch, or replace each other. • Example- The silver coating on spoons. • Decomposition Reaction- the breaking down of complex substances into simpler ones. • Example- Carbonation in Soda WHAT ARE AN ELEMENT’S CHEMICAL PROPERTIES? • Chemical Property- a way of describing a substance by how it reacts to other substances. • Reactivity- an ability of a substance to undergo a chemical change. • How an atom reacts is determined by its placement on the periodic table. • The elements in the first column are the most reactive • Stable- atoms that rarely react. • The last column (the noble gasses) as the most stable. • The reactivity is determined by the number of Rubidium is in the first column of the electrons in its outer layer, the fewer electrons, periodic table so it is very reactive. the more reactive it is. WHAT IS A MOLECULE? • Molecule- when atoms bond covalently with one another, they form a group of atoms. • The atoms are so tightly bonded that they act like a single particle. • Elements and compounds can be made of molecules. • Molecules of a given substance are always alike. • Ionic compounds are not made of molecules, they collections of ions held together. WHAT IS AN ACID? • Acids- have properties that help define what they are. • Indicator- a safe way to see if something is acidic. A substance that changes color in the presence of an acid or a base. • Example- Litmus Paper • Properties: • Sour Taste (only taste when it is safe to) • Corrosiveness (can wear away metal and burn skin) • React with metals (that’s why batteries get crusty) WHAT IS A BASE? • Bases- a groups of compounds that share special properties. • Many bases are poisonous and can burn skin. • Properties • Bitter Taste • Slippery when touched • Dissolve hair, wool, grease, and fingernails WHAT ARE EXOTHERMIC AND ENDOTHERMIC REACTIONS? • Exothermic Reactions- chemical reactions that give off heat. • Not all produce a flame, some release energy in smaller amounts more slowly. • Endothermic Reactions- chemical reactions that absorb energy. • They require a constant supply of energy. Ice melting is an Welding is an endothermic reaction. exothermic reaction. CHEMICAL FORMULA ACTIVITY.