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Earth Chemistry Chapter 4 Page 80 Matter • Anything that has mass and takes up space • Atoms are matter 132 Physical Properties Physical properties describe matter Some are observed through the senses: – Shape, color, odor, texture Some can be measured – Melting point, strength, hardness – ability to conduct • electricity (conductivity) • magnetism • or heat Density is a physical property D= m/v •Measured in units of g/cm3 • Density is how much matter something has for its volume • Another way to say it is . . . how heavy something is for its size 136B • Density is mass divided by volume 135 Example: If 10cm3 of ice has a mass of 9.17g, what is the density of ice? Mass m=9.17g Volume = 10cm3 Density is m/v 9.17g 10cm3 = 0.917 g/cm3 135 137B Physical properties help determine uses • Why is copper used in electric power lines? • Why is Styrofoam used for coffee cups? 138 Chemical properties • Determine how a substance will react • Generally not as easy to observe as physical properties • The chemical composition changes A chemical property describes how a substance changes into a new substance Either by: • Combining with other elements • Breaking apart into new substances 139 Chemical properties include: • Reactivity • Flammabilityability to burn 139 Characteristic properties help to identify and classify substances • Characteristic Properties are the physical or chemical characteristics the substance is known for Example: • Helium is light and non-flammable so it is good for blimps element • A substance that cannot be separated or broken down into simpler substances by chemical means • More than 90 elements occur naturally on Earth Atoms are made of • Protons • Neutrons • Electrons Parts of an Atom • Atoms are made of protons, neutrons and electrons Particle Proton Charge +1 Neutron 0 Electron -1 Mass 1 (1.67*10-27) 1 (1.67*10-27) 0 (9.00*10-31) Location In the nucleus In the nucleus Moving around outside the nucleus Elements are classified by the number of protons their atoms contain, which is their atomic number. This box tells us the atomic number is 1. 1 H 1.00797 • This means it has one proton (and so 1 electron) • The bottom number is the mass number. • H, hydrogen, has a mass of 1.00797. # of protons= # of electrons (In a neutral atom) Neutral Atoms • The charge of an atom is usually neutral • The number of protons equals the number of electrons • Ex. C (carbon) atomic number of 6, so 6 protons and 6 1 H 1.00797 Mass Number • The mass number equals the number of protons and the number of neutrons. • Mass number = protons + neutrons • The mass number of Carbon is 12.0107 C 12.0107 6 WS Lesson 23—126 points Hints: • Spell Correctly • Symbol is 1 Capital 1 small or 1 Capital • Round mass • Three columns are the same – Atomic Number * – Protons * – Electrons * • Neutrons=Mass-Protons Isotope An atom with a different number of neutrons is called an isotope Hydrogen usually is a proton and an electron If it has a neutron it is considered an isotope hydrogen neutrons deuterium tritium 0 1 neutron 2 neutrons Half-lives • The rate of decay of an isotope is called the half-life. A half life is the amount of time it takes for half of the amount to decay. It is constant • Different elements have different halflives Radium-226=1620 years Uranium-238 = 4.5 billion years Average Atomic Mass • Because the isotopes of an element have different masses the periodic table uses average atomic mass • Amu---atomic mass unit • Found by calculating the weighted average of the atomic masses of the naturally occurring isotopes Isotopes of Carbon • Notice they have the same number of protons, different numbers of neutrons Bohr's Planetary Model • Electrons orbit the nucleus like planets orbiting the sun. • The orbits called electron shells or orbitals • close to the nucleus hold fewer electrons than those far away. Valence Electrons and Periodic Properties • Elements in the periodic table are arranged in columns based on similarities in their chemical properties • These columns are called groups Valence Electrons • Valence electrons are the electrons in the outermost energy level • Every atom has between one and eight valence electrons 154 Electrons dictate the many properties of a material including chemical reactivity and physical attributes, like taste, texture, appearance and color. Obscertainer Lab