1. Matter Chapter 2, Section 1

2. Elements and the Periodic Table Element – a substance that cannot be broken down into simpler substances by ordinary chemical or physical means There are more than 112 known elements, and new elements continued to be discovered 92 elements occur naturally, the others are produced in laboratories The rows in the periodic table are called periods, and the columns are called groups Of the known elements, only eight make up most of Earth’s continental crust (Oxygen, Silicon, Aluminum, Iron, Calcium, Sodium, Potassium, and Magnesium); six of which are metals

5. Concept Check What is an element? A class of matter that contains only one type of atom; an element cannot be broken down, chemically or physically, into a simpler substance with the same properties.

6. Atoms An atom is the smallest particle of matter that contains the characteristics of an element The central region of an atom is called the nucleus; the nucleus contains positive charged protons and neutrons, which have no electrical charge; negatively charged electrons orbit the nucleus Protons and neutrons have the same mass Atomic Number – the number of protons in the nucleus of an atom Atoms have the same number of protons as electrons An electron is the smallest of the 3 fundamental particles in an atom, with a mass of about 1/1836 the mass of a proton or neutron Energy Level – one of several distinct regions around the nucleus of an atom where electrons are located

7. Two Models of an Atom

8. Concept Check How are electrons, protons, and neutrons alike and how are they different? They are all subatomic particles that make up atoms. Protons have positive electrical charges, neutrons have no charge, and electrons have negative charges. Protons and neutrons are found in an atom’s nucleus. Electrons move about the nucleus.

9. Isotopes Atoms of the same element always have the same number of protons, but the number of neutrons for atoms of the same element can vary Isotope – an atom with the same number of protons but different numbers of neutrons for a given element; an isotope’s mass number is different from that of a given element Mass Number – the number of protons and neutrons in the nucleus of an atom The nuclei of most atoms are stable, but many elements have atoms whose nuclei are unstable; radioactive decay occurs when the forces that hold the nucleus together are not strong enough

10. Carbon Isotopes

11. Concept Check What are isotopes? Atoms of the same element with the same number of protons but different numbers of neutrons.

12. Why Atoms Bond Most elements exist combined with other elements to form substances with properties that are different from the elements themselves Compound – a substance formed by the chemical combination of two or more elements in definite proportions and usually having properties different from those of its constituent elements Compounds form when atoms are more stable (exist at a lower energy state) in a combined form The chemical process, called bonding, centers around the electron arrangement of atoms When an atom’s outermost energy level does not contain the maximum number of electrons, the atom is more likely to form a chemical bond with one or more atoms Chemical Bond – a force that holds together atoms that form a compound

13. Chemical Bonding of Sodium and Chloride

14. Concept Check Why do compounds form? Compounds form as a result of changes in the arrangement of electrons in the outermost shells of the bonded atoms.

15. Types of Chemical Bonds An atom that gains electrons becomes negatively charged, and an atom that loses electrons becomes positively charged, because the number of protons and electrons are no longer equal Ion – an atom or a molecule that possesses an electric charge Oppositely charged ions attract each other to form crystalline compounds Ionic Bond – a bond that forms between negative and positive ions Covalent Bond – a bond that forms when atoms share electrons The smallest particle of a covalent compound that shows the properties of that compound is a molecule Metallic Bond – a bond that forms when electrons are shared by metal ions

16. Ionic Bonds

17. Covalent Bonds

18. Metallic Bonds

19. Concept Check What happens when two or more atoms react? Electrons are gained, lost or shared when two or more atoms react to form a compound.

20. Assignment Read Chapter 2, Section 1 (pg. 34-43) Read Chapter 2, Section 1 (pg. 34-43) Do Section 2.1 Assessment #1-10 (pg. 43) Do Section 2.1 Assessment #1-10 (pg. 43)