Chapter Three Atoms and the Periodic Table Lesson 3-1 Inside the Atom • An atom consists of a nucleus surrounded by one or more electrons. • The central core is the nucleus. • The smallest particles inside the nucleus are protons and neutrons. • The energetic particles moving in all directions around the nucleus are electrons. 3-1 • Protons carry (+) a positive charge. • Neutrons are neutral – they carry no electrical charge. • An electron carry (-) a negative charge. Protons and Neutrons have the approximately the same mass. The Atom Electrons Protons _ + Nucleus _ + Neutrons 3-1 • The atomic number is the number of protons in its nucleus. • The number of protons equals the number of electrons. This creates a balanced charge, making a neutral atom. 3-1 • Because atoms are so small, scientists have created the atomic mass (amu) to measure the particles of the atoms. • The mass of a proton is about one atomic mass unit. It takes almost 2,000 electrons to equal one atomic mass unit. 3-1 Electrons • Electrons move so rapidly in the space around the nucleus that is impossible to know exactly where any electron is at a particular time. • The electrons in an atom aren’t all the same distance away from the nucleus. ONLY the electrons that are the FURTHEST from the nucleus are involved in bonding. 3-1 Valance Electrons • The electrons involved in bonding are called valance electrons. • A chemical bond forms between two atoms when valence electrons move between them. Electrons may be transferred from one atom to another, or they may be shared between the atoms. • One way to show the number of valence electrons is with an electron dot diagram. It includes the symbol for an element surrounded by dots. Each dot stands for one valence electron. Oxygen O 3-1 8 (atomic number) O (symbol) Oxygen (element name) 15.999 (mass) 3-1- # of Protons 8 (atomic number) O (symbol) Oxygen (element name) 15.999 (mass) The number of protons equals the atomic number. Oxygen has 8 protons. 3-1 # of Electrons 8 (atomic number) O (symbol) Oxygen (element name) 15.999 (mass) The number of electrons = the number of protons. Oxygen has 8 protons, therefore, oxygen has 8 electrons. 3-1 # of Neutrons 8 (atomic number) O (symbol) Oxygen (element name) 15.999 (mass) The number of neutrons = mass number – atomic number. Mass of oxygen = 15.999 Atomic # of O = - 8.000 # of neutrons = 7.999 round off : Oxygen = 8 neutrons 3-1 You Try: 36 (atomic number) Kr (symbol) Krypton (element name) (mass) 83.80 • Number of protons? • Number of electrons? • Number of neutrons? 3-1 You Try Answer • Krypton has 36 Protons. • Krypton has 36 Electrons. • Krypton has 48 neutrons. (round off: 84 - 36 = 48) 3-1 Paying Attention? ? Ni Nickel 59 • If Nickel has 28 protons and 28 electrons, what is the atomic #? 3-1 Finding the Atomic Mass 28 Ni Nickel ?? • If the protons = 28 and the neutrons = 31, what is the atomic mass? • Add the two together: 28 + 31 = 59. 3-1 • The arrangement of the periodic table is by increasing atomic mass. • Mendeleev was the first person to arrange the elements in a pattern. • Each row going across the periodic table is called a period. Quiz Review 1. 2. 3. 4. 5. 6. 7. 8. Know how to label an element box: (atomic number, symbol, name, and atomic mass). Know the diagram of an atom. Know how the periodic table is arranged. Know what a period is. Know the first person to arrange the elements in a pattern. Know how to find the number of neutrons. How to determine the atomic number with given information. Know how to figure out the atomic mass with given information. *Extra credit: Who is afraid of Krypton?* Lesson Two 3-2 Organizing Elements 3-2 Organizing Elements • Mendeleev noticed that patterns appeared when the elements were arranged in order of increasing atomic mass. – The atomic mass of an element is the average mass of one atom of the element. – In the periodic table, the properties of the elements repeat in each row,or period, of the table. 3-2 Organizing the Elements • The modern periodic table contains over 100 squares, one for each element, arranged in order of atomic number. • An element’s properties can be predicted from its location in the periodic table. – The elements in a column are called a group,or family. The groups are numbered 1-18. Elements in each group have similar characteristics. – Each horizontal row of the table is called a period. The elements in a period are not alike in properties. There are seven periods. – The periodic table works because it’s based on the structure of atoms, especially the valence electrons. The number of valence electrons that an element has increases from left to right across a period. Lesson 3-3 Metals 3-3 Metals • Most of the elements are metals, which are found to the left of the zig-zag line in the periodic table. • Chemists classify an element as a metal based on physical properties such as: hardness, shininess, malleability, and ductility. – Malleable means to pound into shape. – Ductile means that the material can be pulled or drawn into a long wire (copper). – Many metals are good conductors of electricity – Gold is the best conductor of electricity, however, it is not used because of its value. 3-3 Metals • Metals show a wide range of chemical properties. – Some metals are reactive. They combine with other elements and compounds quickly, and give off energy. – A metal can wear away – this is called corrosion (rust is a chemical reaction). 3-3 Metals • The metals in a group, or family, have similar properties, and these properties change gradually as you move across the table. – Group One – Alkali metals: Highly reactive - so reactive they are never found uncombined in nature. – Group Two – Alkaline Earth Metals: reactive, but not as reactive as alkali metals, also not found uncombined in nature. – Group 3 – Group 12 – Transition Metals: They form a bridge between the very reactive metals on the left and the less reactive metals on the right. – Group 13-16 – includes metals, non-metals, and metalloids. The metals in this group are not nearly reactive as those on the left side of the periodic table. – The elements on the bottom of the periodic table are called lanthanides and actinides. They are known as rare earth elements. Nonmetals and Metalloids Lesson 3-4 3-4 • Nonmetals are elements that lack most of the properties of metals. The nonmetals are located to the right of the zig-zag line in the periodic table. • Physical Properties – nonmetals: – – – – Dull Low density Brittle Poor conductors of electricity. 3-4 • Many metals and nonmetals react with each other. • Many nonmetals also form molecules of two identical atoms, O2. • Molecules containing two atoms are called diatomic molecules. 3-4 Element Families • • • • • The elements in group 14, the Carbon Family, have atoms with 4 valence electrons. Carbon is the only nonmetal in the group. The elements in group 15 is the Nitrogen Family. Each element in the nitrogen family has 5 valence electrons. The two non-metals are phosphorus and nitrogen. The elements in group 16, the Oxygen Family, have 6 valence electrons. These atoms typically gain or share two atoms in a reaction. The Oxygen we breath is O2 and Ozone = O3. Group 17 is known as the Halogen Family. All but one of these elements in the Halogen Family are nonmetals. A halogen atom has 7 valence electrons and typically gains or shares one electron when it reacts. Group 18 is known as the Nobel Gases. These elements do not ordinarily form compounds, because the Nobel gases do not share or gain electrons. 3-4 • Hydrogen is the simplest element. Its atoms generally contain only one proton and one electron. Hydrogen is not grouped in a family – it is on its own because hydrogen’s chemical properties are so different from the other elements. 3-4 • On the border between the metals and the nonmetals are seven elements called metalloids. • The metalloids have some of the characteristics of metals and some of the characteristics of nonmetals. • The most useful property of the metalloids is their varying ability to conduct electricity. – Some metalloids are used to make semiconductors. Semiconductors are substances that under some conditions can carry electricity, and under other conditions cannot. Semiconductors are used to make computer chips, transistors, and lasers.