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Explore the fundamental properties of elements, atoms, and chemical bonds. Understand how elements combine to form substances and the importance of balanced chemical equations. Learn about the different forms of energy and the concepts of conduction, convection, and radiation. Discover the forces of gravity and friction, and the difference between speed and velocity.
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Elements • Elements are the basic building blocks of matter. • There are 115 known elements. • This number changes as new elements are created in research labs. • 90 elements occur in nature and fewer than half of them are common.
Elements Continued • Elements are listed on the Periodic Table of Elements by atomic number (number of protons). • Elements are composed of atoms.
Atoms • Atoms are the smallest particle of an element that has the properties of that element. • John Dalton (1803)- Modern atomic theory. • All atoms of a particular element are alike, but they are different from the atoms of any other element.
Atoms Continued • Atoms are made up of protons, neutrons and electrons (subatomic particles). • Protons have a positive charge (+) • Electrons have a negative charge (-) • Neutrons have no charge
Atoms Continued • Protons and neutrons make up the nucleus of an atom. • Electrons orbit (circle) the nucleus. • Move around the nucleus in shells or energy levels. • The further away from the nucleus a shell is, the more electrons it can hold and therefore it has a higher energy level. • The inner most level can hold 2 electrons, the second can hold 8, the third up to 18 and so on. • The outer most shell (valence) can hold no more than 8 electrons.
The Periodic Table • Elements are arranged by atomic number (number of protons in the nucleus). • Vertical columns are called groups or families. • Horizontal rows are called periods. • Elements located in the same group have similar electron configurations (same number of valence electrons). Therefore they will react in similar ways.
Changes in Matter • Scientists know of millions of different substances in the world. • How is this possible if there are only 115 known elements? • Elements combine to form different substances.
Chemical Bonds • Atoms are held together in molecules by chemical bonds. • Chemical bonds store energy.
Ionic Bonds • Ions are formed when an atom gains or loses an electron to become + or -. • Sodium (Na) can lose its valence electron to form a sodium ion (Na+). • Chlorine (Cl) can gain an electron to form a chlorine ion (Cl-). • An ionic bond is formed when two ions of opposite charges (metal and nonmetal) are attracted to each other and form a new substance. • NaCl: Sodium Chloride (table salt).
Covalent Bonds • Covalent bonds are formed between atoms of two nonmetals. • Electrons are shared. • Example: Carbon can share electrons with 2 oxygen atoms (1 with each) to form carbon dioxide (CO2). • Covalent bonds are stronger than ionic bonds because of this sharing of electrons.
pH • The pH scale refers to strength of an acid or a base. • The scale ranges from 0-14. • 0 is the most acidic. (hydrochloric acid) • 14 is the most basic. (sodium hydroxide) • 7 is neutral. (water)
Chemical Equations Continued • Chemical equations must be balanced. This means that each element appears the same number of times in both the reactants and products. • Example: C + O2 CO2
If there are different amounts of each element on either side of an equation we must balance it using coefficients. • Example: H2 + O2 H2O This is not balanced. To balance we add coefficients. 2 H2 + O2 2 H2O
States of Energy • Potential Energy (PE) – Stored energy • Gasoline (chemical) • Rock on a cliff (position) • Food (chemical) • Coal (chemical)
Kinetic Energy (KE) – energy an object has when it is moving. • Falling rock • Thrown ball • Runner • Waterfall
Conduction • Conduction is the transfer of heat by direct molecular contact. • Metals are good conductors of heat. • Example: If you hold a metal rod in fire the heat will quickly distribute between the molecules in the rod and it will become hot.
Convection • Convection is the transfer of heat by the flow of a liquid or a gas. • Warm air in a room rises and cool air sinks. This causes a circular motion called a convection current.
Radiation • Radiation is the transfer of heat through space in the form of waves. • Heat from the sun travels through the vacuum of space to reach Earth.
What is Force? • A force is a push or pull that is exerted on an object. • Force stops motion: gloved hand catching a ball • Force slows motion: friction slowing a skateboard • Force changes direction: tennis racket striking a tennis ball
Gravity • Law of Universal Gravitation states that in the universe every mass attracts every other mass. • Greater mass = greater gravitational force • An apple falls to Earth because the Earth is much more massive.
Friction • Friction is a force that resists motion. • It must be overcome to start an object moving and/or to keep it moving. • Rougher surface+Heavy object = More friction • Smooth surface+Light object = Less friction
Speed and Velocity • Speed and velocity are terms used to describe the motion of an object. • Speed is the distance traveled over a certain period of time. • Velocity is the same but includes a specific direction (north, east, southwest, etc.)
The equation used to determine both speed and velocity is distance divided by time. • S = d/t V = d/t • Units for measuring speed/velocity: Kilometers/hour (km/hr) Miles/hour (mi/hr) Feet/second (ft/s) Meters/minute (m/min) Centimeters/second (cm/s)
Acceleration • Acceleration is the rate in change in velocity. • Can be used to describe increased or decreased (deceleration) change. • Acceleration is calculated by subtracting an object’s starting velocity from it’s final velocity and dividing by time. • A = vf – vs / t
Motion of falling objects • Gravity causes objects released above Earth’s surface to fall to the ground. • Mass, size and shape of the object determines how fast it will fall. • Air resistance (air drag) also affects falling objects. • In a vacuum (no air) all objects will fall at the same rate because gravity is the only force acting on them.
Spheres • The Earth consists of 3 spheres: • The lithosphere (rock sphere) • The hydrosphere (water sphere) • The atmosphere (gas sphere) These are smaller parts of the Biosphere: The place where all life exists on Earth.
Interaction of Air, Land, and Water • Weathering is the breaking down of rocks into smaller pieces. • Physical weathering: water seeps into cracks in rock and freezes, the water expands, breaking the rock apart. • Chemical weathering: oxygen and water chemically react with iron mineral in rocks, turning to rust, which crumbles away easily.
Erosion • Erosion is the process by which rock material at Earth’s surface is removed and carried away. • Erosion requires a moving force (like water). • Example: Streams and rivers turn a muddy brown after a heavy rain due to the rock material in the water. • Glaciers and wind can also contribute to erosion.
Structure of the Earth • The Earth is composed of 3 layers. • The crust: outermost layer (5-50 km) • The mantle: middle layer (~2900 km) • The core: innermost layer • Outer core (~2300 km) • Inner core (~1200 km): Thought to be solid
Theory of Continental Drift • 1912: Alfred Wegener proposed the continents were drifting across Earth’s surface. • Based on how the shapes of the continents fit together like a puzzle. • The original “super continent” was called Pangea.
Plate Tectonics • Earth’s crust is broken into pieces, or plates, that slowly move and interact at their boundaries in various ways. • Caused by heat circulating in the mantle. • There are 10 major plates: The Pacific, North American, Nazca, Cocos, South American, African, Arabian, Eurasian, Indian, and Antarctic.
Plate Interactions • As the plates move, some are colliding, some are spreading apart, and some are sliding past one another. • Subduction zone: When an oceanic plate collides with a continental plate it tends to slide down under it. This forms mountains and volcanoes. • Fault zones: When one plate slides sideways past another. This sometimes causes severe earthquakes.
Earth’s Geologic History • Scientists have pieced together much of Earth’s history by studying rocks. • There are 3 main rock types: • Sedimentary • Igneous • Metamorphic
Sedimentary Rock • Most commonly formed by the deposition of particles underwater. (dirt being submerged) • About 75% of land surface is covered with sedimentary rocks.
Igneous Rock • Form from hot molten rock material, either underground (magma) or on Earth’s surface (lava) • Volcanoes
Metamorphic Rock • Form from pre-existing rocks that undergo changes caused by extreme heat and/or pressure. • Plate motions
Distances in Space • Distances in space are so great they are difficult to comprehend. • The distance between Earth and the nearest star (besides the sun) is 41,000,000,000,000 km. (41 trillion) • We use light-years to express distances in space. • A light-year is the distance light travels in a year.
The Big Bang Theory • According to this theory, all the matter and energy that exists in the universe today was once concentrated in a very small, dense object about the size of an atom. • For some unknown reason this object suddenly expanded creating the beginning of space and time. • Matter continued to move away and over time small amounts combined to form stars and planets.
