1. General Chemistry Chapter 2 Definitions Left click your mouse to continue.

2. DIRECTIONS This slide show presentation is designed to function like flash cards. To check your answer, and/or to move on to the next slide, simply left click your mouse.

3. ALLOTROPIC MODIFICATIONS (ALLOTROPES) Different forms of the same element in the same physical state

4. ANHYDROUS Without water

5. ANION A negative ion

6. ATOM The smallest particle of an element that maintains its chemical identity through all chemical and physical changes. Fundamentally consists of: electrons, protons and neutrons Atom contains equal numbers of protons and electrons Atoms are components of molecules

7. ATOMIC MASS UNIT (AMU) One twelfth of the mass of an atom of the carbon-12 isotope; a unit used for stating atomic and formula weights

8. ATOMIC NUMBER The number of protons in the nucleus of an atom. An atom contains an equal number of electrons and protons.

9. ATOMIC WEIGHT Weighted average of the masses of the constituent isotopes of an element; the relative mass of atoms of different elements.

10. AVOGADRO’S NUMBER 6.02 x 10 23 of the specified items.

11. CATION A positive ion.

12. CHEMICAL FORMULA Combination of symbols that indicates the chemical composition of a substance.

13. COMPOSITION STOICHIOMETRY Describes the quantitative (mass) relationships among elements in compounds.

14. EMPIRICAL FORMULA The smallest whole-number ratio of atoms present in a compound; Also known as the simplest formula

15. FORMULA Combination of symbols that indicates the chemical composition of a substance

16. FORMULA UNIT The smallest repeating unit of a substance- for non-ionic substances, the molecule

17. FORMULA WEIGHT The mass, in atomic mass units, of one formula unit of substance. Numerically equal to the mass, in grams, of one mole of the substance. This number is obtained by adding the atomic weights of the atoms specified in the formula.

18. HYDRATE A crystalline sample that contains water and another compound in a fixed mole ratio. Ex: CuCO 4.5H 2 O

19. ION An atom or group of atoms that carries an electrical charge. A positive ion is a cation; a negative ion is an anion Ions are formed when neutral atoms lose or gain electrons

20. IONIC COMPOUND A compound that is composed of cations and anions. EX: NaCl

21. LAWS OF CONSTANT COMPOSITION Different samples of a pure compound always contain the same elements in the same proportions by mass; this corresponds to atoms of these elements in fixed numerical ratios. Also known the Law of Definite Proportions

22. LAW OF MULTIPLE PROPORTIONS When two elements, A and B, form more than one compound, the ratio of the masses of element B that combine with a given mass of element A in each of the compounds can be expressed by small whole numbers.

23. MOLAR MASS The mass of substance in one mole of the substance; numerically equal to the formula weight of the substance Units= g/mol

24. MOLE 6.02 x 10 23 formula units (or molecules, for a molecular substance) of the substance under discussion. The mass of one mole, in grams, is numerically equal to the formula (molecular) weight of the substance.

25. MOLECULAR FORMULA A formula that indicates the actual number of atoms present in a molecule of a molecular substance.

26. MOLECULE The smallest particle of an element or compound that can have a stable independent existence. Atoms are components of molecules, and molecules are the components of many elements and most compounds

27. MOLECULAR WEIGHT The mass, in atomic mass units, of one molecule of a nonionic (molecular) substance. Numerically equal to the mass, in grams, of one mole of such a substance. This number is obtained by adding the atomic weights of the atoms specified in the formula.

28. MONATOMIC Consisting of a single atom. The noble gases exist as monatomic molecules. Chlorine gas is not monatomic Cl 2

29. PERCENT COMPOSITION The mass percentage of each element in a compound.

30. PERCENT PURITY The percentage of a specified compound or element in an impure sample.

31. POLYATOMIC Consisting of more than one atom. Elements such as Cl 2, P 4 and S 8 exist as polyatomic molecules. Examples of polyatomic ions are ammonium ion, NH 4 +, and sulfate ion, SO 4 -2

32. STOICHIOMETRY Description of the quantitative relationships among elements in compounds and among substances as they undergo chemical changes

33. STRUCTURAL FORMULA A representation that shows how atoms are connected in a compound.

34. DALTON’S ATOMIC THEORY 1.An element is composed if extremely small indivisible particles called atoms. 2.All atoms of a given element have identical properties, which differ from those of other elements. 3.Atoms cannot be created, destroyed, or transformed into atoms of another element. 4.Compounds are formed when atoms of different elements combine with each other in small whole- number ratios. 5.The relative numbers and kinds of atoms are constant in a given compound.

35. Diatomic Molecules O 2, H 2, N 2, F 2, Cl 2, Br 2, I 2 There are two atoms in each of these molecules.

36. 1 mole =? particles 6.02 x 10 23 particles 1 mol He = 6.02 x 10 23 He atoms 1 mol H 2 = 6.02 x 10 23 H 2 molecules –Because this is a diatomic molecule, 1 mol H 2 = 2(6.02 x 10 23 ) H 2 atoms