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

DensityDensity is a physical property Density is how much matter something has for its volume Another way to say it is... how heavy something is for its size Density is mass divided by volume D= m/v Measured in units of g/cm 3 136B135

Example: If 10cm 3 of ice has a mass of 9.17g, what is the density of ice? Mass m=9.17g Volume = 10cm 3 Density is m/v 9.17g  10cm 3 = g/cm 3 135

Physical properties Physical properties help determine uses Why is copper used in electric power lines?copper Why is Styrofoam used for coffee cups? 137B 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 Flammability- ability to burn 139

Characteristic properties help to identify and classify substances identify 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 blimpsHelium

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 Atoms are made of Protons Neutrons Electrons

Parts of an Atom Atoms are made of protons, neutrons and electrons ParticleChargeMassLocation Proton+11 (1.67*10 -27) In the nucleus Neutron01 (1.67*10 -27) In the nucleus Electron0 (9.00*10 -31) 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. This means it has one proton (and so 1 electron) The bottom number is the mass number. H, hydrogen, has a mass of H

# 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 electrons H

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 C

WS Lesson 23 —126 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 0 neutrons deuterium 1 neutron tritium2 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 half- lives 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