Section 3.1 What are Elements?

What are elements? What are elements? • The physical world that surrounds you and all living things are composed of matter. • Matter is anything that has volume and mass. • On Earth, matter usually can be found as a solid, liquid, or gas. What are elements? Elements • All matter is made of substances called elements. • An element is a substance that cannot be broken down into simpler substances by physical or chemical means. • Ninety-two elements occur naturally on Earth and in the stars. • Other elements have been produced in laboratory experiments. What are elements? Elements • Each element is identified by a one-, two-, or three-letter abbreviation known as a chemical symbol. What are elements? Elements are Made of Atoms • Each element has distinct characteristics. • An atom is the smallest particle of an element that has all of the characteristics of that element. • All atoms consist of even smaller particles: protons, neutrons, and electrons. What are elements? Elements are Made of Atoms • The nucleus, which is made up of protons and neutrons, forms the center of an atom. – A proton (p+) is a tiny particle that has mass and a positive electrical charge. – A neutron (n0) is a particle with about the same mass as a proton, but it is electrically neutral; that is, it has no electrical charge. • All atomic nuclei have a positive charge. What are elements? Elements are Made of Atoms • The number of protons and neutrons in different atoms varies widely. – The atomic number is the number of protons in an atom’s nucleus. – The mass number is the combined number of protons and neutrons. What are elements? Elements are Made of Atoms What are elements? Elements are Made of Atoms • Surrounding the nucleus of an atom are smaller particles called electrons. • An electron (e–) has little mass, but it has a negative electrical charge that is exactly the same magnitude as the positive charge of a proton. • An atom has an equal number of protons and electrons which produces an atom that has no overall charge. What are elements? Elements are Made of Atoms • An energy level represents the area in an atom where an electron is most likely to be found. • The mass of an atom depends mostly upon the number of protons and neutrons in its nucleus. • The size of an atom depends upon the number and arrangement of its electrons. What are elements? Electrons in Energy Levels • Electrons are distributed over one or more energy levels in a predictable pattern. • Each energy level can hold only a limited number of electrons. – The innermost energy level can hold only 2 electrons. – The second energy level can hold up to 8 electrons. – The third energy level can hold up to 18 electrons. – The fourth energy level can hold up to 32 electrons. • Electrons tend to occupy the lowest available energy level. What are elements? Electrons in Energy Levels • The number of electrons in the outermost energy level determines the chemical behavior of the different elements. • Valence electrons are the outermost electrons in an atom. • Elements with the same number of valence electrons have similar chemical properties. What are elements? Electrons in Energy Levels • Sodium (Na) atoms, with just one valence electron, are highly reactive metals, which means that they combine easily with other elements. What are elements? Electrons in Energy Levels • Elements such as helium (He), neon (Ne), and argon (Ar) are inert, which means that they do not easily combine with other elements. • This is because they have full outermost energy levels. What are elements? Isotopes • The number of neutrons in the nuclei of an element’s atoms can vary. • Isotopes are atoms of the same element that have different mass numbers and the same chemical properties. • The atomic mass of an element is the average of the mass numbers of the isotopes of an element. What are elements? Isotopes • The nuclei of some isotopes are unstable and release radiation. • Radioactivity is the spontaneous process through which unstable nuclei emit radiation. • During radioactive decay, a nucleus can lose protons and neutrons, change a proton to a neutron, or change a neutron to a proton. • Because the number of protons in a nucleus identifies an element, decay changes the identity of an element. What are elements? What Elements are Most Abundant? • The two most abundant elements in the universe are hydrogen and helium. What are elements? What Elements are Most Abundant? • The percentages of elements in Earth’s crust differ from the percentages in the universe. What are elements? WARM UP - you have until 2:15 • Copy down the vocabulary words below. All can be found in the glossary! • Take one of the blue books on your desk and write your name in the front cover and place it in your notebook in the hand out section. • Take a Adopt an atom work sheet and place it in your notebook as well. Vocabulary – energy level – element – neutron – valence electron – atom – atomic number – isotope – nucleus – mass number – atomic mass – proton – electron – radioactivity How Atoms Combine Objectives • Describe the chemical bonds that unite atoms to form compounds. • Relate the nature of chemical bonds that hold compounds together to the physical structures of compounds. • Distinguish among different types of mixtures and solutions. Vocabulary – copy down! Until 2:15 – compound – ion – solution – chemical bond – ionic bond – acid – covalent bond – chemical reaction – base – molecule What are elements? REVIEW Electrons in Energy Levels What are elements? REVIEW Section Assessment 1. Match the following terms with their definitions. ___ A proton ___ D energy level ___ C neutron ___ B atom A. a tiny particle that has mass and a positive electrical charge B. the smallest particle of an element that has all of the characteristics of that element C. a tiny particle that has mass and is electrically neutral D. an area of an atom where an electron is most likely to be found How Atoms Combine Compounds • A compound is a substance that is composed of atoms of two or more different elements that are chemically combined. • Most compounds have totally different properties from the elements they are made of. • For most elements, an atom is chemically stable when its outermost energy level is full. • Chemical bonds are the forces that hold the elements together in a compound creating a state of stability. How Atoms Combine Compounds Covalent Bonds – One way in which atoms fill their outermost energy levels is by sharing electrons. – A covalent bond is the attraction of two atoms for a shared pair of electrons that holds the atoms together. How Atoms Combine Compounds Covalent Bonds – A molecule is composed of two or more atoms held together by covalent bonds. – Molecules have no overall electrical charge b/c the number of electrons is equal to total number of protons. How Atoms Combine Compounds Covalent Bonds How Atoms Combine Compounds Polar Molecules – When atoms in a covalent bond do not share electrons equally, they form polar bonds. – Polar bonds have a positive end and a negative end. – The overall shape of a molecule indicates whether it is polar. How Atoms Combine Ions • Sometimes, atoms gain or lose electrons from their outermost energy levels. • A charged particle called an ion is an atom that gains or loses an electron. • In general, an atom in which the outermost energy level is less than half-full tends to lose its valence electrons. • When an atom loses its valence electrons, it becomes positively charged. How Atoms Combine Ions • An atom in which the outermost energy level is more than half-full tends to fill its outermost energy level by adding one or more needed electrons. • Such an atom forms a negative ion. • If the outermost energy level is exactly halffull, an atom may form either a positive or negative ion. How Atoms Combine Ions Ionic Bonds – Positive and negative ions attract each other. – An ionic bond is the attractive force between two ions of opposite charge. – Positive ions are always written first in chemical formulas. How Atoms Combine Chemical Reactions • Sometimes, compounds break down into simpler substances. • A chemical reaction is the change of one or more substances into other substances. • Chemical reactions are described by chemical equations. • A chemical equation must be balanced by showing an equal number of atoms for each element on each side of the equation. How Atoms Combine Mixtures and Solutions • A mixture is a combination of two or more components that retain their identities. • When a mixture’s components are easily recognizable it is called a heterogeneous mixture. – Example: Soil • In a homogeneous mixture the component particles cannot be distinguished, even though they still retain their original properties. – Example: Coffee How Atoms Combine Mixtures and Solutions • A homogeneous mixture is also called a solution. • A solution may be liquid, gaseous, or solid. – EXAMPLES: – Seawater is a liquid solution consisting of water molecules and ions of many elements that exist on Earth. – Air is a solution of gases, mostly nitrogen and oxygen molecules together with other atoms and molecules. – Bronze is a solid solution of copper and tin atoms. How Atoms Combine Mixtures and Solutions Acids and Bases – Many chemical reactions that occur on Earth involve solutions called acids and bases. – An acid is a solution containing a substance that produces hydrogen ions (H+) in water. – The most common acid in our environment is carbonic acid, which is produced when carbon dioxide is dissolved in water by the following reaction. H2O + CO2 → H2CO3 How Atoms Combine Mixtures and Solutions Acids and Bases – The most common acid in our environment is carbonic acid, which is produced when carbon dioxide is dissolved in water by the following reaction. H2O + CO2 → H2CO3 – Some of the carbonic acid molecules in the water dissociate, or break apart, into hydrogen ions and bicarbonate ions, as represented by the following equation. H2CO3 → H+ + HCO2– How Atoms Combine Mixtures and Solutions Acids and Bases – Bases produce hydroxide ions (OH–) in solution. – A base can neutralize an acid by combining with hydrogen ions of the acid to form water through the following reaction. H+ + OH– → H2O – The pH scale measures the hydrogen and hydroxide ions in solutions on a scale of 0 to 14, with 7 being neutral. How Atoms Combine Mixtures and Solutions Acids and Bases – The pH scale measures the hydrogen and hydroxide ions in solutions on a scale of 0 to 14, with 7 being neutral. – A solution with a pH reading below 7 is considered to be acidic. – A solution with a reading above 7 is considered to be basic. How Atoms Combine Section Assessment 1. Match the following terms with their definitions. ___ C covalent bond A. an atom that gains or loses an ___ D compound ___ A ion ___ B acid electron and becomes electrically charged B. a solution containing a substance that produces hydrogen ions in water C. an attraction of two atoms for a shared pair of electrons that hold the atoms together D. a substance that is composed of atoms of two or more different elements that are chemically combined How Atoms Combine Section Assessment 2. Identify whether the following are acidic, basic, or neutral. A Milk ___ A. Acidic C Distilled water ___ B. Basic A Rainwater ___ C. Neutral B Ammonia ___ A Lemon ___ A Tomato ___ B Antacid ___ How Atoms Combine Section Assessment 3. Describe the following chemical equation: S + O2 → SO2 One sulfur atom reacts with one oxygen molecule to yield one molecule of sulfur dioxide. States of Matter Objectives • Describe the states of matter on Earth. • Explain the reasons that matter exists in these states. • Relate the role of thermal energy to changes of state in matter. Vocabulary • crystalline structure • plasma • glass • condensation • evaporation • sublimation States of Matter Solids • Solids are substances with densely packed particles, which may be ions, atoms, or molecules, depending upon the substance. • The particles of a solid are arranged in a definite pattern; thus, a solid has both a definite shape and a definite volume. • Most solids have a crystalline structure, in which the particles are arranged in regular geometric patterns. States of Matter Solids • Crystals form symmetrical solid objects with flat faces and straight edges between faces. • The angles between the faces depend upon the internal arrangement of the particles. States of Matter Solids • When many crystals form in the same space at the same time, mutual interference results in a mass of intergrown crystals, called a polycrystalline solid. • Most solid substances on Earth, including rocks, are polycrystalline materials. • Glasses are solids that consist of densely packed atoms arranged at random. • Glasses do not form crystals, or their crystals are so small that they cannot be seen. States of Matter Liquids • The atoms in solids vibrate at any temperature above absolute zero (2273°C). • These thermal vibrations increase with increasing temperature. • At the melting point of the material, the vibrations break the forces holding the solid together. • The particles can then slide past each other, and the substance becomes liquid. • While liquids do not have their own shape, they do have definite volume. States of Matter Gases • Individual particles in a liquid may gain sufficient energy to escape the liquid. • Evaporation, or vaporization, is the process of changing from a liquid to a gas. • When any liquid reaches its boiling point, it vaporizes quickly and becomes a gas. • Sublimation is the slow change of state from a solid to a gas without an intermediate liquid state. States of Matter Gases • In gases, the particles are separated by relatively large distances and move about at extremely high speeds. • Gas particles move independently of each other and travel randomly. • Gases have no definite shape or volume and can expand into any space available, unless they are restrained. • Earth’s gravity keeps the gases in the atmosphere from escaping into space. States of Matter The Electromagnetic Spectrum • Satellites detect different wavelengths of energy reflected or emitted from Earth’s surface. • This energy has both electric and magnetic properties and is referred to as electromagnetic radiation. • Electromagnetic radiation includes visible light, gamma rays, X rays, ultraviolet waves, infrared waves, radio waves, and microwaves. States of Matter Plasma • At temperatures greater than 5000°C, the collisions between particles are so violent that electrons are knocked away from atoms. • Such extremely high temperatures exist in stars, and, as a result, the gases of stars consist entirely of positive ions and free electrons. • Plasmas are hot, highly ionized, electrically conducting gases. States of Matter Changes of State • Solids melt when they absorb thermal energy and their temperatures rise. • When a liquid absorbs thermal energy from the environment, it evaporates. • When a liquid freezes, the same thermal energy is then released back into the environment. • When a gas is cooled, it releases thermal energy in the process of condensation. • Condensation is the change from a gas to a liquid. States of Matter Conservation of Matter and Energy • The law of conservation of matter states that matter cannot be created or destroyed but can change from one form to another. • The law of the conservation of energy, also called the first law of thermodynamics, states that energy cannot be created or destroyed but it can be changed from one form to another. States of Matter Section Assessment 1. Match the following terms with their definitions. ___ C crystalline structure A. solids that consist of densely packed atoms arranged at ___ A glasses random ___ D evaporation B. a slow change from a solid ___ B sublimation to a vapor without an intermediate liquid state C. a solid in which the particles are arranged in regular geometric patterns D. the process of change from a liquid to a gas States of Matter Section Assessment 2. What are two examples of matter in the plasma state that you have seen? Lightning and the matter inside a neon tube are in the plasma state. States of Matter Section Assessment 3. Identify whether the following processes absorb or release energy into the environment. ___ B condensation A. Absorb energy ___ A evaporation B. Release energy ___ A melting C. Neither release or absorb ___ B freezing ___ A sublimation Chapter Resources Menu Study Guide Section 3.1 Section 3.2 Section 3.3 Chapter Assessment Image Bank Section 3.1 Study Guide Section 3.1 Main Ideas • The basic building blocks of matter are atoms. Atoms consist of protons, neutrons, and electrons. • Protons have a positive electrical charge, electrons have a negative electrical charge, and neutrons are electrically neutral. Protons and neutrons make up the nucleus of an atom; electrons surround the nucleus in energy levels. • An element is a substance consisting of atoms with a specific number of protons in their nuclei. Isotopes of an element differ by the number of neutrons in their nuclei. Many elements are mixtures of isotopes. • The number of electrons in the outermost energy levels of atoms determines their chemical behavior. Elements with the same number of electrons in their outermost energy levels have similar chemical properties. Section 3.2 Study Guide Section 3.2 Main Ideas • Atoms of different elements combine to form compounds. • Atoms held together by the sharing of electrons in covalent bonds form molecular compounds. • Ions are electrically charged atoms or groups of atoms. Positive and negative ions attract each other and form ionic compounds. • Acids are solutions containing hydrogen ions. Bases are solutions containing hydroxide ions. Acids and bases can neutralize each other. • A mixture is a combination of components that retain their identities. A solution is a mixture in which the components can no longer be distinguished as separate. Solutions can be liquid, solid, gaseous, or combinations. Section 3.3 Study Guide Section 3.3 Main Ideas • Matter on Earth exists in three common physical states: solid, liquid, or gaseous. Matter in the universe includes plasma. • Most solids have a crystalline structure. • Liquids are densely packed arrangements of particles. • Gases consist of widely separated, individual particles. Plasmas are hot, highly ionized, electrically conducting gases. • Changes of state involve thermal energy. Chapter Assessment Multiple Choice 1. Which of the following is NOT about elements? a. They cannot be broken down into simpler substances by physical or chemical means. b. There are 47 naturally occurring elements on Earth and in the stars. c. All matter is made of elements. d. Each element is identified by a chemical symbol. There are 92 elements that occur naturally on Earth and in the stars. Chapter Assessment Multiple Choice 2. An element’s atomic number represents ____. a. the number of protons in the atom’s nucleus b. the combined number of protons and neutrons in the atom’s nucleus c. the number of neutrons in the atom’s nucleus d. none of the above The combined number of protons and neutrons is the element’s mass number. The number of neutrons can vary among the atoms of an element, creating isotopes. Chapter Assessment Multiple Choice 3. Which is the most abundant element in the universe? a. oxygen c. iron b. helium d. hydrogen Hydrogen makes up about 93.5% of all matter in the universe. It is followed by helium at 6.3%. Chapter Assessment Multiple Choice 4. Which is the most abundant element in Earth’s crust? a. hydrogen c. oxygen b. silicon d. aluminum Oxygen makes up 46.65 of Earth’s crust. It is followed by silicon (27.7%), aluminum (8.1%), and iron (5.0%). Chapter Assessment Multiple Choice 5. Which of the following is a molecule? a. argon c. nitrogen b. water d. uranium Argon, nitrogen, and uranium are elements. Chapter Assessment Short Answer 6. What condition is necessary for matter to be in a plasma state? The temperature must be greater than 5000ºC. At temperatures this high, the collisions between particles are so violent that electrons are knocked away from atoms. Chapter Assessment Short Answer 7. What three forms can a solution take? A solution may be liquid, gaseous, or solid. Chapter Assessment True or False 8. Identify whether the following statements are true or false. ______ false A pH value of 11 would indicate an acid. ______ true Ions are atoms that either lost or gained an electron. ______ true Apple juice is an example of a solution. ______ false In a polar bond, electrons are shared equally. ______ false Two negative ions will join to create an ionic bond. 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