MatterMatter

Chapter 2, Section 1Chapter 2, Section 1

Elements and the Periodic TableElements 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

Concept CheckConcept 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.

AtomsAtoms 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

Two Models of an AtomTwo Models of an Atom

Concept CheckConcept CheckHow 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.

IsotopesIsotopes

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

Carbon IsotopesCarbon Isotopes

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What are isotopes?Atoms of the same element with the same

number of protons but different numbers of neutrons.

Why Atoms BondWhy 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

Chemical Bonding of Sodium and Chemical Bonding of Sodium and ChlorideChloride

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Why do compounds form?Compounds form as a result of changes in

the arrangement of electrons in the outermost shells of the bonded atoms.

Types of Chemical BondsTypes 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

Ionic BondsIonic Bonds

Covalent Covalent BondsBonds

Metallic BondsMetallic Bonds

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What happens when two or more atoms react?

Electrons are gained, lost or shared when two or more atoms react to form a compound.

AssignmentAssignment

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)