1. CHEMICAL SYMBOLS, FORMULAS, AND EQUATIONS Looking at water as a molecule made up of atoms, the building blocks of matter

2. Is water a mixture? All matter is made up of atoms. Matter that is made up of only ONE kind of atom is an ELEMENT. Water is NOT an element as it is made up of TWO kinds of atoms—hydrogen and oxygen. And because water’s properties are different from either hydrogen’s or oxygen’s, and the oxygen and hydrogen in water cannot be easily separated, water isn’t considered a mixture either.

3. Compounds Instead, water is considered a COMPOUND—a substance that is composed of the atoms of two or more elements linked together chemically in certain fixed proportions. Chemists have identified more than 24 million compounds.

4. Chemical Formulas Compounds and elements are represented by chemical formulas. You are probably familiar with some of them: H 2 O – water CO 2 – carbon dioxide NaCl – sodium chloride or table salt NH 3 – ammonia

5. What is a substance? A substance is an element or compound that has a uniform and definite composition with distinct properties. The smallest unit of a substance is a MOLECULE. Atoms of a substance are held together by chemical BONDS which act like a “glue”.

6. Molecules Molecules can be formed of one, two, or more atoms of the same or different elements. Oxygen usually occurs as a DIATOMIC molecule, a molecule made up of two oxygen atoms (O 2 ). However, ozone is a molecule made up of 3 oxygen atoms (O 3 ). Other elements that usually occur as diatomic molecules are hydrogen, nitrogen, fluorine, chlorine, bromine and iodine.

7. Elements All known elements are organized into the PERIODIC TABLE OF THE ELEMENTS. To read the table and write chemical formulas, you need to know the ‘language’ chemists use to represent atoms, elements, and compounds. The letters in this language are the CHEMICAL SYMBOLS. Each element is assigned one chemical symbol, with the first letter capitalized and any other letters lowercase. H is the symbol for hydrogen, and Ca is the symbol for calcium.

8. Common Elements and Their Symbols Aluminum – Al Bromine– Br Calcium – Ca Carbon – C Chlorine – Cl Cobalt – Co Copper – Cu Fluorine – F Gold – Au Iodine – I Iron – Fe Lead – Pb Magnesium – Mg Mercury – Hg Nickel – Ni Nitrogen – N Oxygen – O Phosphorus -- P Silver – Ag Sodium – Na Sulfur – S Tin -- Sn

9. Chemical Formulas The words in this chemical language are CHEMICAL FORMULAS. Each chemical formula represents a different chemical substance. Each symbol represents each element present. A number written below the normal line of letters called a subscript tells how many atoms of the element just to its left are in one unit of that substance. If there is no subscript, we know there is just one atom of that element.

10. H 2 O is a chemical formula which tells us that one molecule of water contains two atoms of hydrogen and one atom of oxygen. H 2 O What about propane, C 3 H 8 ? 2 atoms of hydrogen 8 atoms of hydrogen 1 atom of oxygen 3 atoms of carbon

11. Chemical Equations The sentences in this chemical language are the chemical equations. Equations summarize the details of chemical reactions in which atoms become rearranged into new substances (because chemical bonds are broken and reformed). The REACTANTS are the starting substances and their formulas are always written on the left side of the equation, before the arrow. The PRODUCTS are the new substance(s) and their formulas are written on the right side.

12. 2H 2 + O 2 → 2H 2 O reactants products + →

13. Summary The letters of the chemical language are the CHEMICAL SYMBOLS for each element. The words are the CHEMICAL FORMULAS. The sentences are the CHEMICAL EQUATIONS.

14. Vocabulary Mixture Homogeneous Heterogeneous Colloid Suspension Solution Substance Atom Element Compound Molecule Chemical Symbol Chemical Formula Chemical Equation

15. Electrical Nature of Matter Like charges repel Unlike charges attract +++---

16. Protons and Electrons What are these positive and negative charges? Each uncharged (neutral) atom has equal numbers of positively charged particles called PROTONS and negatively charged particles called ELECTRONS. For instance, hydrogen (H) has one proton and one electron; sodium (Na) has 17 protons and 17 electrons. Most atoms also contain neutrally charged NEUTRONS.

17. Ions This “sticky force” of electrical attraction is what holds most atoms together in chemical compounds: the attraction between a proton of one element and an electron of another element. IONS are electrically charged atoms or groups of atoms. Ions are another type of compound besides molecules.

18. IONIC COMPOUNDS Atoms gain or lose electrons to form NEGATIVE or POSITVE ions. Gain electron → Negative ion Lose electron → Positive ion IONIC COMPOUNDS are substances that are composed of positive and negative ions. Ionic compounds have NO net electrical charge; they have the SAME number of positive and negative charges.

19. ANIONS AND CATIONS A negatively-charged ion is called an ANION. A positively-charged ion is called a CATION. An anion can be a single negatively charged ion, like chlorine (Cl - ), or a group of bonded atoms such as a nitrate anion (NO 3 - ). A cation can be a single positively charged ion, like sodium (Na + ), or a group of bonded atoms such as ammonium cation (NH 4 + ). A ion that is a group of bonded atoms is called a POLYATOMIC (many atom) ION.

20. Some common cations and anions Na + sodium Cl - chloride Ca 2+ calcium NO 3 - nitrate SO 4 2- sulfate OH - hydroxide Fe 3+ iron (III) PO 4 3- phosphate

21. Written name Written names of ionic compounds have two parts. You name the cation first, then the anion. For an anion of only one atom, you change the ending to the suffix –ide. For example, the anion formed from F (fluorine) is fluoride (F - ). So KF is called potassium fluoride. CaCO 3 is calcium carbonate. AgNO 3 is silver nitrate.

22. Rules for writing formulas for ion compounds 1)Write the cation first, then the anion 2)The correct formula will contain the FEWEST positive and negative ions needed to make the TOTAL electrical charge zero. 3)When cation and anion charges don’t add up to zero, you have to add ions of either type until the charges balance.

23. 4)Some metal atoms form ions with one charge under certain conditions and another charge under different conditions. To specify the electric charge for these ions, Roman numerals are used in parentheses after the metal’s name. Iron (III) is Fe 3+ while Copper (II) is Cu 2+. FeO is iron (II) oxide, otherwise known as rust.

24. Practice problems Copy this table in your foldable and complete it, for the six substances on p. 41 using the information on Table 1.4 in your textbook on p. 40. CationAnionFormulaName Sample K+K+ Cl - KCl Potassium chloride CaSO 4 Ammonium nitrate Al 3+ SO 4 2- Magnesium hydroxide Ca 2+ CO 3 2-