Chapter 8 lesson 1Electrons and energy levels By Miss CatieBrumit & Mrs. Shaw
The periodic table Review • The periodic table has 115 blocks- one for each known element • Each block has the basic properties of the element like its state of matter at room temperature and its atomic number. • The atomic number is the number of protons in an atom of each element. • Each block also has an elements atomic mass or the average mass of all the isotopes of that element.
Periods and Groups Review • You can learn about the elements on the periodic table based on its location. • The elements are organized into periods (rows) and groups (columns) • The periodic table lists the elements in order of atomic number increasing left to right across a period • Elements in the each group have similar chemical properties and react with other elements in similar ways
Metals, Non-metals, & Metalloids Review • The three main elements on the periodic table are metals non metals and metalloids • Except hydrogen, all the elements on the left side of the table are metals. • Non metals are on the right side and Metalloids are the stair step or zigzag region between metals and nonmetals. Metals Metalloids Nonmetals
Atoms bond • A chemical bond is a force that holds two or more atoms together. These chemical bonds hold compounds together. • In nature, pure elements are rare. Instead, atoms of different elements combine to form compounds. • Compounds make up most matter, even in living and non living things.
Electron number & arrangement • The exact location of an electron cannot be determined because the electrons are always in motion around the nucleus. However the electrons in each of the elements is usually in a certain area of space around the nucleus. • Some of the electrons are closer to the nucleus while some are farther away
Electrons and energy • Different electrons in an atom have different amounts of energy. The distance that the electron moves around the nucleus corresponds with its level of energy. • Electrons that are closest to the nucleus have the least amount of energy. Electronsfarthest from the nucleus have the most amount of energy. • Only two electrons can be in the lowest energy level. But the second energy level can hold up to 8.
Lewis Dot Diagram of Carbon showing only the valence electrons Bohr Model of electrons
Electrons and bonding • Think about having two magnets. The closer they are to each other the stronger the attraction is. There is a similar attraction between the negatively charged electrons and the positively charged nucleus. • The outermost electrons (valence electrons) can be attracted to the nucleus of other atoms. This attraction is what causes a chemical bond.
Let’s practice . . . • Where are the electrons with the most energy found in an atom? • How many electrons can the first shell hold? the second shell? • What causes one atom to be attracted to another?
Let’s practice . . . Answers • Where are the electrons with the most energy found in an atom? The electrons with the most energy are found farthest from the nucleus • How many electrons can the first shell hold? the second shell? The first shell holds 2 and the second shell holds 8 • What causes one atom to be attracted to another? The negative charge of the valence electrons in one atom are attracted to the positive charge of a nucleus in another atom.
Valence electrons 1 • The outer most electrons are the only electrons involved in chemical bonding. • A valance electron is an outermost electron of an atom that participates in chemical bonding. Valence electrons have the most energy out of all the electrons in an atom. • The number of valence electrons in each atom of an element can help determine the type and the number of bonds It can form.
Periods • Each row is called a “period” • The elements in each period (row) have the same number of shells 1st Period = 1 Shell 2nd Period = 2 Shells 3rd Period = 3 Shells 4th Period = 4 Shells www.chem4kids.com
Groups Group 8 = 8 electrons Group 1 = 1 electron Except for He, it has 2 electrons Group 2 = 2 electrons • Each column is called a “group” 3,4,5,6,7 • Each element in a group has the same number of electrons in their outer orbital, also known as “shells”. • The electrons in the outer shell are called “valence electrons” www.chem4kids.com
Transition Metals • Transition Metals have slightly different rules for shells and valence electrons. • This is something you will learn about in High School Chemistry. www.chem4kids.com
Electron dot diagrams • The electron dot diagram is a model that represents valence electrons in an atom as dots around the element’s chemical symbol. They help predict how an atom will bond with other atoms. • Dots representing valence electrons, are placed one-by-one on each side of an element’s chemical symbol until all the dots are used. Some dots will be paired up; others will not. The number of unpaired dots is often the number of bonds an atom can form.
Practice with Electron Dot Diagrams How many valence electrons does each element have? How many bonds can each element form? • Hydrogen Valence: Bonds: • Neon Valence: Bonds: 3. Calcium Valence: Bonds: 4. Sulfur Valence: Bonds: 5. Aluminum Valence: Bonds:
Practice with Electron Dot Diagrams How many valence electrons does each element have? How many bonds can each element form? • Hydrogen Valence: 1 Bonds: 1 (1 shell) • Neon Valence: 8Bonds: 0 - stable 3. Calcium Valence: 2 Bonds: 6 4. Sulfur Valence: 6 Bonds: 2 5. Aluminum Valence: 3 Bonds: 5
Nobel gases • The elements in group 18 are Nobel gases. • Except for helium, nobel gases have eight valence electrons and are chemically stable. • Chemically stable atoms usually don’t react or form bonds easily with other atoms.
Stable and Unstable atoms • Atoms with unpaired dots in their electron dot diagrams are reactive, or chemically unstable. • Many atoms become more stable by forming chemical bonds with other atoms. • When an atom forms a bond, it gains, loses or shares valence electrons with the other atom(s). The most stable atoms have 8 valence electrons.
Chemical bonding Chemical bonding is the joining of atoms to form new substances. A chemical bond is an interaction that holds two atoms together. Most atoms form bonds by gaining, losing, or sharing valence electrons until they fill their outer shell to become “happy”.
Types of Chemical Bonds There are two types of chemical bonds we will discuss: ionic bonds and covalent bonds.
Covalent Bonds Covalent bonds happen when atoms share electrons. For example: Chlorine needs one electron to have a full outer shell so it can share 2 electrons with another Chlorine atom and become stable.
Covalent Bonds Another very important covalent bond is H + H + O = H2O
Ionic Bonds Ionic bonds happen when electrons are transferred from one atom to another, causing the atom to become either positively charged or negatively charged. Na + Cl= Na Cl Table Salt
Review of concepts • http://quizlet.com/8092253/science-exam-3-3-labels-diagrams-flash-cards/ • http://www.youtube.com/watch?v=wWUYHHo-zB0&feature=related • http://www.youtube.com/watch?v=y6QZRBIO0-o