12 II. The Periodic TableDewey Decimal Classification system helps you find a book quickly and efficiently.
13 Periodic tablePeriodic table is a chart of elements to help chemists to organize and display the elements.
14 Element symbol is a shorthand that chemists use to save time and space. Eg:H is the symbol for hydrogen.O is the symbol for oxygen.
15 The rows in the table are called periods. The elements in a row have the same number of energy levels.
16 The columns in the table are called groups The elements in a group have similar properties.
17 III. Identifying Characteristics NucleusNeutronProtonThe number of electrons equals to the number of protons.ElectronAll the atoms of an element are exactly alike.Different elements are made of different kinds of atoms.
18 All the atoms of an element have the same number of protons. eg:The oxygen atoms in water, air or plants all contain 8 protons in their nucleus.The atoms of different elements have different number of protons.eg: iron atoms all contain 26 protons in their nucleus.
19 The number of protons in the atom of the element equals to atomic number. Ex: how many protons in the atoms of the following elements?Carbon (2nd period, 14th group)Sodium (3rd period, 1st group)Radon (6th period, 18th group)Answer:61186
20 For one element, the number of neutrons can be different. eg: all atoms of H element contain 1 proton in the nucleus.Some H atoms contain no neutron while others contain 1 or 2 neutrons in their nucleus.Atoms of the same element that have different numbers of neutrons are called isotopes.
21 mass number = nproton+ nneutron An atom’s mass number is the number of protons plus the number of neutrons it contains.Isotope of hydrogenprotiumdeuteriumtritiumProtonNeutronMass Numbermass number = nproton+ nneutron
22 ex 1: Oxygen have three types of atoms which contain 7, 8, 9 neutrons respectively. Isotope of oxygen123Proton8Neutron79Mass NumberDifferent isotopes of the element are referred to using its mass number.Eg: O-15, O-16, O-17
27 Multiple choiceTrue or false (if it is false, correct it)Filling tables.Filling blanks. (probably)Match.Short answers.Calculation. (atomic mass )Paper dictionary, calculator are allowed.
28 Atomic mass is the weighted average mass of the isotopes of an element. 75.8%24.2%If you have 100 chlorine atoms, 75.8% of them are Cl-35 and 24.2% are Cl-37.What’s the atomic mass of Cl?Atomic mass of chlorine =75.8%×34.97u+24.2%×36.97u=35.45 u u – atomic mass unitChlorine17Cl35.453
29 IV. Classification of Elements Three general categories of elements——metals, metalloids and nonmetals.MetalloidsMetalsnonmetalsMost of the elements are metals, they are found on the left side of the periodic table.
30 1. Metals The properties of metals: Most with high melting point (solid →liquid)Metallic lusterGood conductor of heat and electricityMalleableDuctile
31 Think about the uses of these properties of metal: Goodconductorof heatMalleableLusterGood conductorof electricityDuctile
32 2. Nonmetals The properties of nonmetals: Usually gases or brittle solids at room temperature.Dull in appearance.Poor conductors of heat and electricity.
33 Can you find this element? All nonmetals are gases and brittle solids at room temperature except one.Can you find this element?bromine
34 Nonmetals are essential for life. Can you find out the nonmetals in protein?
35 3. MetalloidsMetalloidsMetalsThe elements between metals and nonmetals are metalloids (semimetals).NonmetalsSilicon are used to make the electronic circuits in electronic devices.
36 Metalloids share some properties with metals and some with nonmetals. The properties of metalloids:Slight luster, conduct electricity at high temperature;Brittle, does not conduct electricity at low temperature.
37 Oxygen is the most abundant element in Earth’s crust. Aluminum is the most abundant metal element in Earth’s crust.
38 ExercisesThe nucleus of one atom contains 12 protons and 12 neutrons, while the nucleus of another atom contains 12 protons and 16 neutrons. What are the atoms?A) chromium atomsB) two different elementsC) two isotopes of an elementD) negatively charged2. What are the majority of the elements on the periodic table called?A) metalsB) metalloidsC) nonmetalsD) compounds
39 3. Which element is a metalloid? A) bromineB) siliconC) potassiumD) ironProblem:4. An atom contains seven electrons and seven protons. What element is this atom? Explain your answer.Nitrogen, because the nitrogen atom has 7 protons.5. Cobalt-60 and cobalt-59 are isotopes. How can they be the same element but have different mass numbers?Different neutron number.