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Earth Chemistry Section 1: Matter Preview • Objectives • Comparing Physical and Chemical Properties • Properties of Matter • Atomic Structure • Parts of the Atom • Atomic Number • Periodic Table Overview • Atomic Mass • Valence Electrons and Periodic Properties Section 1 Earth Chemistry Section 1 Objectives • Compare chemical properties and physical properties of matter. • Describe the basic structure of an atom. • Compare atomic umber, mass number, and atomic mass. • Define isotope. • Describe the arrangement of elements in the periodic table. Earth Chemistry Section 1 Properties of Matter • matter * • Every object in the universe is made up of particles of matter. The amount of matter in any object is the mass of that object. • All matter has two types of distinguishing properties-*. Earth Chemistry Section 1 Properties of Matter, continued • Physical properties are characteristics that can be observed without changing the composition of the substance. • Physical properties include density, color, hardness, freezing point, boiling point, and the ability to conduct an electric current. • Chemical properties are characteristics that describe how a substance reacts with other substance to produce different substances. Earth Chemistry Section 1 Properties of Matter, continued Elements • element a substance that cannot be separated or broken down into simpler substances by chemical means; • Each element has a characteristic set of physical and chemical properties that identify it. • Every known element is represented by a symbol of one or two letters. Earth Chemistry Section 1 Properties of Matter, continued Atoms • Elements are made of atoms. • atom * • A single atom is so small that its size is difficult to imagine. Earth Chemistry Section 1 Atomic Structure • Even though atoms are very tiny, they are made up of smaller parts called subatomic particles. • There are three types of subatomic particles—protons, electrons, and neutrons. • proton * • electron * • neutron * Earth Chemistry Section 1 Atomic Structure, continued The Nucleus • The protons and neutrons of an atom form the nucleus. • The positively charged nucleus makes up most of an atom’s mass but very little of its volume. The volume of an atom is mostly empty space. The Electron Cloud • The electrons of an atom move in a certain region of space called an electron cloud that surrounds the nucleus. • The negatively charged electrons are attracted to the positively charged nucleus. This attraction holds electrons in the atom. Earth Chemistry Parts of the Atom Section 1 Earth Chemistry Section 1 Atomic Number • The number of protons in the nucleus of an atom is called the atomic number. • All atoms of any given element have the same atomic number. An element’s atomic number sets the atoms of that element apart from the atoms of all other elements. • Elements on the periodic table are ordered according to their atomic numbers. • Elements in the same column on the periodic table have similar arrangements of electrons in their atoms, and therefore have similar chemical properties. Earth Chemistry Section 1 Atomic Number, continued The diagram below shows the atomic numbers and mass numbers of three elements. Earth Chemistry Atomic Number, continued The diagram below shows the periodic table. Section 1 Earth Chemistry Periodic Table Overview Section 1 Earth Chemistry Section 1 Atomic Mass • The sum of the number of protons and neutrons in an atom is the mass number. • The mass of a subatomic particle is too small to be expressed easily in grams, so a special unit called the atomic mass unit (amu) is used. • Protons and neutrons each have an atomic mass close to 1 amu. • Electrons have much less mass than protons or neutrons do. The mass of 1 proton is equal to the combined mass of about 1,840 electrons. Earth Chemistry Section 1 Atomic Mass, continued Isotopes • Although all atoms of a given element contain the same number of protons, the number of neutrons may differ. • isotope * • Because of their different number of neutrons and their different masses, different isotopes of the same element have slightly different properties. Earth Chemistry Section 1 Atomic Mass, continued Average Atomic Mass • Because isotopes of an element have different masses, the periodic table uses an average atomic mass of each element. • The average atomic mass is the weighted average of the atomic masses of the naturally occurring isotopes of an element. Earth Chemistry Section 1 Valence Electrons and Periodic Properties • Based on similarities in their chemical properties, elements on the periodic table are arranged in columns, which are called groups. • An atom’s chemical properties are largely determined by the number of the outermost electrons in an atom’s electron cloud. These electrons are called valence electrons. • The elements that form each group commonly have the same number of valence electrons. Earth Chemistry Section 1 Valence Electrons and Periodic Properties, continued • When an atom has 8 valence electrons, it is considered stable, or chemically unreactive. Unreactive atoms do not easily lose or gain electrons. • Elements whose atoms have only one, two, or three valence electrons tend to lose electrons easily. These elements have metallic properties and are generally classified as metals. • Elements whose atoms have from four to seven valence electrons are more likely to gain electrons. Many of these elements are classified as nonmetals.