12/6/16 The Nature of Matter 1
12/6/16 Matter & Energy Matter • Matter is the "stuff" of the universe. • Matter is anything that occupies space and has mass . • Matter exists as a solid, liquid, gas, and plasma . • Matter may be changed both physically and chemically . • The Law of Conservation of Matter states that matter cannot be created or destroyed, only changed . 2
12/6/16 Energy • Energy has no mass, does not take up space, and can only be measured by its effects on matter . • Energy is commonly defined as the ability to do work or to put matter into motion . • When energy is actually doing work, it is referred to as kinetic energy . • When energy is inactive or stored, it is called potential energy . • All forms of energy exhibit both kinetic and potential work capacities. Forms of Energy 3
12/6/16 Chemical Energy • Chemical energy is the energy stored in the bonds of chemical substances . • When the bonds are broken the stored potential energy is released for use . • It becomes kinetic energy, or energy in action that causes an effect on matter. Electrical Energy • Electrical energy is energy that results from the movement of charged particles . • In your body, an electrical current is generated when charged particles, called ions, move across cell membranes. 4
12/6/16 Mechanical Energy • Mechanical energy is directly involved in moving matter . • As the muscles in your legs shorten, they pull on your bones, causing your limbs to move. Radiant Energy • Radiant energy is energy that travels in waves . • It is the energy of the electromagnetic spectrum, which includes X rays and infrared, light, radio, and ultraviolet waves . 5
12/6/16 Atoms Atoms • Matter consist of atoms. • An atom is the smallest unit of matter that has the chemical properties of that element . • Atoms cannot be broken down into smaller particles . 6
12/6/16 The Structure of an Atom • Atoms are made up of small parts called protons, electrons, and neutrons . • Protons are particles that have a positive (+) electrical charge . • Neutrons are particles that are neutral (o), they have no charge . • Electrons are particles that have a negative (-) electrical charge . The Nucleus of an Atom • The protons and neutrons of an atom are packed close to one another and form the nucleus . • The nucleus has a positive charge because protons have a positive charge and neutrons have no charge. • The nucleus makes up most of an atom’s mass . 7
12/6/16 Electrons • The electrons of an atom move in a certain area of space called an electron cloud that surrounds the nucleus . • Because opposite charges attract each other, the negatively charged electrons are attracted to the positively charged nucleus. • This attraction is what holds electrons in the atom. Structure of Atoms 8
12/6/16 Atomic Mass • The total number of protons and neutrons in an atom is its atomic mass . • Electrons have much less mass than protons and neutrons. • It would take 1,840 electrons to equal the mass of one proton . Atomic Number • The number of protons in the nucleus of an atom is called the atomic number . • All elements have their own atomic number. • Since atoms have to have an equal number of protons and electrons, the atomic number is also equal to the number of electrons in an atom . 9
12/6/16 Atomic Numbers & Masses • Atomic Number = the number of protons or the number of electrons . • Atomic Mass = the number of protons and neutrons . Isotopes • An atom that has more neutrons than protons is called an isotope . • Isotopes of the same element will have slightly more mass because of the different numbers of neutrons . 10
12/6/16 Radioactive Isotopes • Some isotopes are radioactive, meaning that their nuclei are unstable and break down at a constant rate over time. • Radioactive isotopes have a number of important scientific and practical uses. • In medicine radioactive isotopes are used as tracers so doctors can view the path of a substance through the body . • Geologists determine the ages of rocks and fossils by analyzing the isotopes found in them . Electron Energy Levels • The electrons occupy a specific space around the nucleus of an atom. • This space is called energy levels, energy shells, and electron shells . • An atom’s chemical properties are determined by the number of the electrons in the energy level furthest away from the nucleus . • There are 7 energy levels and each level can hold a certain number of electrons . 11
12/6/16 Energy Levels • Energy Level 1 is the closest to the nucleus and can only hold 2 electrons . • Energy Level 2 can hold a maximum of 8 electrons . • Energy Level 3 can hold up to 18 electrons . • All the other energy levels hold larger and larger numbers of electrons. Elements • An element is a substance that cannot be broken down into simpler substances by chemical means . • Each element has physical and chemical properties that can be used to identify it. • Of the 118 elements that have been identified, approximately 98 elements occur naturally on Earth . • Eight of these 98 elements make up more than 98% of Earth’s crust . • To classify the elements the Periodic Table is used. 12
12/6/16 Periodic Table • Elements on the periodic table are arranged according to their atomic numbers . • Elements in the same column on the periodic table have similar arrangements of electrons in their atoms. • Elements that have similar arrangements of electrons have similar chemical properties . 13
12/6/16 How It’s Organized The periodic table is organized like a big grid. • The elements are placed in specific places because of the • way they look and act . Groups & Periods In the Periodic Table, there are Periods (left to right) • and Groups (up and down). Each Period and each Group means something different . • 14
12/6/16 Groups The elements in a GROUP have the same number of • electrons in their outer energy level . Every element in the first column (Group #1) has one • electron in its outer energy level. Every element on the second column (Group #2) has two • electrons in the outer energy level. Periods Each row (left to right) is called a PERIOD. • Elements that are in the same Period have the same • number of energy levels . 15
12/6/16 Families Scientists group families of elements by their • chemical properties and how the elements react with the outside world. Alkaline Metals • Alkaline Earth Metals • Transition Elements • Halogens • Inert Gasses • Metals Almost 75% of all elements are classified as metals . • Any substance with high electrical conductivity, luster, • and malleability, and easily loses electrons to form positive ions. Metals are also defined by their position on the Periodic • Table These groups include alkaline metals, alkaline earth • metals, transition metals, and rare earth metals. 16
12/6/16 Alkalaline Metals Alkaline metals are found in • Group 1 (excluding hydrogen). These elements are very • reactive. They all have one electron in • their outer energy level . That's one electron away from • being stable. Examples include lithium, • sodium, potassium, and rubidium . Alkalaline Earth Metals Alkaline earth metals are found • in Group 2 . These elements are somewhat • reactive. They all have two electrons in • their outer energy level . That's two electrons away from • being stable. Examples include beryllium, • magnesium, calcium, and strontium . 17
12/6/16 Transition Elements Transition metals are able to • put more than eight electrons in the energy level that is one in from the outermost one . Examples include silver, • gold, copper, nickel, zinc, and platinum . Halogens The halogen family is Group 7 • on the periodic table. Halogens are all just one • electron shy of having full energy levels . Because they are so close to • being stable, they will combine with many different elements . They will often bond with • metals. Examples include fluorine, • chlorine, bromine and iodine . 18
12/6/16 Inert Gasses All of the inert gases have • full outer energy levels with eight electrons . They are all in Group 8 and • they will not react with any other element. Examples include helium, • neon, argon, and krypton . Compounds and Bonds 19
12/6/16 Chemical Compounds • In nature, most elements are found combined with other elements in compounds. • A chemical compound is a substance formed by the chemical combination of two or more elements in definite proportions . • Scientists show the composition of compounds by a kind of shorthand known as a chemical formula . • Water (dihydrogen monoxide), which contains two atoms of hydrogen for each atom of oxygen, has the chemical formula H 2 O. Chemical Compounds • The formula for table salt is NaCl. • This indicates that the elements - sodium and chlorine - combine in a 1:1 ratio. • Sodium is a silver-colored metal that is soft enough to cut with a knife and reacts explosively with cold water. • Chlorine is a very poisonous, greenish gas. • Sodium and chlorine combine to form sodium chloride (NaCl), or table salt. • Sodium chloride is a white solid that dissolves easily in water. 20
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