Looking for Patterns in Chemical Reactivity

1. Looking for Patterns in Chemical Reactivity

2. Elements and Compounds • An element is a pure substance that cannon be broken down into simpler substances by ordinary means such as a chemical reaction. (Iron, Oxygen, and Carbon are all elements.) • A compound is a pure substance made up of two or more elements that are chemically combined (Water, or H2O, is a compound.)

3. The Periodic Table of Elements

4. Atoms and Subatomic Particles • All atoms are composed of protons, neutrons, and electrons. • Protons are positively charged particles found in the nucleus of an atom. • Neutrons are uncharged particles that are also found in the nucleus. • Electrons are negatively charged particles that orbit the nucleus of an atom.

5. Atoms and Subatomic Particles • Protons and Neutrons are about the same size and mass. • Electrons are much smaller than Protons and Neutrons. • Protons and Electrons have charges that are equal in size but opposite in sign.

6. Some Notation

7. Atomic Number and Atomic Mass • Atomic number is the number of protons and electrons in each atom of that element • The atomic mass is the number of protons and neutrons in an atom (these make up the nucleus of an atom) • By subtracting the atomic number from the atomic mass you can find the number of neutrons

8. Isotopes • An isotope of an element has the same atomic number but different mass numbers because the number of neutrons has changed. • For example: we can have Carbon-12 with 6 protons and 6 neutrons but we can also have Carbon-14 with 6 protons and 8 neutrons

9. Metals, Non-metals, and Metalloids

10. Properties of Metals, Non-metals, and Metalloids Malleable – able to be pounded or formed into a shape Ductile – able to be drawn into a wire

11. Organization of the Periodic Table • The periodic table arranged elements into periods (horizontal rows) and groups (vertical columns) according to their atomic numbers. • Elements in the same group have similar chemical properties.

12. Electron Shells

13. Electron Shell Patterns • Period 1 elements have a single electron shell, while Period 2 elements have two electron shells and Period 3 elements have 3 electron shells. • The first electron shell can hold two electrons while the second and third shells can each hold eight electrons. • Elements in the same group have the same number of electrons in their outermost shell.

14. Predicting Chemical Reactivity • Electron shell diagrams are useful because they show the number of electrons in the outer shells. • Knowing this is the key to understanding the organization of the periodic table and the chemical properties of elements. • Elements in the same group have similar chemical properties because they have the same number of electrons in their outer shell.

15. Families Within the Periodic Table

16. Valence Electrons • Knowing the number of outer shell electrons will help us predict the formation of compounds, name the compounds, and write their chemical formulas. • The outer shell is called the valence shell and the electrons that occupy it are called valence electrons. • A chemical bond forms between two atoms when their valence electrons form a stable arrangement together.

17. Valence Electrons • The chemical properties of elements are related to the energy changes that take place when their atoms lose, gain, or share electrons to obtain a filled valence shell. • Metals are elements that tend to lose their valence electrons relatively easily and this accounts for many of their physical and chemical properties. • One important property of valence shells is that they generally like to be full.

18. Ions • Any atom or group of atoms that carries an electrical charge is called an ion. • When a neutral atom gives up one or more electrons, the positively charged ion that results is called a cation. • HINT: cation – think t or + for positive • When a neutral atom gains one or more electrons, the negatively charged ion that results is called an anion. • HINT: anion – think n for negative

19. Cations • Adding energy to a neutral sodium atom removes its one valence electron and leaves a positively charged sodium ion (cation) and a free electron.

20. Anions • Adding an electron to a neutral chlorine atom results in a negatively charged chlorine ion (anion) and the release of energy.

21. Electron Dot Diagrams • Electron dot diagrams depict valence electrons as dots. • The inner electrons and the atomic nuclei are represented by the symbol for the element and dots are placed one at a time moving around the symbol.