Flashcards Chapter 2 Chemistry Notes

Kinetic Molecular Theory

• All matter is composed of tiny particles.
• The particles are in constant motion.
• Increased temperature reflects increased motion of particles.
• Solids, liquids, and gases differ in the freedom of motion of their particles and in how strongly the particles attract each other.

Solid

• Constant shape and volume.
• The particles are constantly moving, colliding with other particles, and changing their direction and velocity.
• Each particle is trapped in a small cage whose walls are formed by other particles that are strongly attracted to each other.
• Friction of moving parts causes temperature to rise.
• As temperature rises, particles move faster and bump harder.
• Neighboring particles are pushed farther apart, and the solid expands.
• If the lubricating or cooling system fails, engine expansion may cause a piston to jam in the cylinder.
• Moving particles bump and tug one another but stay in the same small space.
• Particles constantly moving.
• Up to 70% of volume occupied by particles…30% empty.
• Strong attractions keep particles trapped in cage.
• Constant collisions that lead to changes in direction and velocity.
• Constant volume and shape due to strong attractions and little freedom of motion.

Liquid

• Constant volume but variable shape.
• The particles are moving fast enough to break the attractions between particles that form the walls of the cage that surround particles in the solid form.
• Each particle in a liquid is constantly moving from one part of the liquid to another.
• Particles move fast enough for attractions to be constantly broken and reformed.
• Particles are less organized, with slightly more space between them than in the solid.
• Particles move throughout the container.
• Particles constantly moving.
• Up to 70% of volume occupied by particles…30% empty
• Attractions are strong but not strong enough to keep particles from moving throughout the liquid.
• Constant collisions that lead to changes in direction and velocity.
• Constant volume, due to significant attractions between the particles that keeps the particles at a constant average distance, but not constant shape, due to the freedom of motion.

Evaporation

• A particle on the surface of a liquid gets a sharp triple kick.
• The kick propels the particle out of the liquid.
• It is traveling too fast for the attractions to the liquid particles to draw it back, so it is now a gas particle.

Gas

• Variable shape and volume.
• Large average distances between particles.
• Little attraction between particles.
• Constant collisions between particles, leading to constant changes in direction and velocity.
• Because particles are so far apart, there is usually no significant attraction between them.
• Particles move in straight paths, changing direction and speed when they collide.
• Particles constantly moving in straight-line paths
• About 0.1% of volume occupied by particles…99.9% empty.
• Average distance between particles is about 10 times their diameter.
• No significant attractions or repulsions.
• Constant collisions that lead to changes in direction and velocity.
• Variable volume and shape, due to lack of attractions and a great freedom of motion.
• You can see an animation that shows the particle nature of solids, liquids, and gases at https://preparatorychemistry.com/KMT_Canvas.html

The Chemical Elements

• Names and Symbols for Elements:
  • aluminum (Al), gold (Au), oxygen (O)
  • argon (Ar), helium (He), phosphorus (P)
  • barium (Ba), hydrogen (H), platinum (Pt)
  • beryllium (Be), iodine (I), potassium (K)
  • boron (B), iron (Fe), silicon (Si)
  • bromine (Br), lead (Pb), silver (Ag)
  • cadmium (Cd), lithium (Li), sodium (Na)
  • calcium (Ca), magnesium (Mg), strontium (Sr)
  • carbon (C), manganese (Mn), sulfur (S)
  • chlorine (Cl), mercury (Hg), tin (Sn)
  • chromium (Cr), neon (Ne), uranium (U)
  • copper (Cu), nickel (Ni), xenon (Xe)
  • fluorine (F), nitrogen (N), zinc (Zn)
• 118 Known Elements
  • 83 are stable and found in nature. Many of these are very rare.
  • 7 are found in nature but are radioactive.
  • 28 are not natural on the earth
    • 2 or 3 of these might be found in stars.

The Periodic Table of the Elements

• Group Numbers on the Periodic Table
• Group Names
  • Alkali Metals
  • Alkaline Earth Metals
  • Halogens
  • Noble Gases
• Metals, Nonmetals, and Metalloids

Characteristics of Metallic Elements

• Metals have a shiny metallic luster.
• Metals conduct heat well and conduct electric currents in the solid form.
• Metals are malleable. For example, gold, Au, can be hammered into very thin sheets without breaking.

Classification of Elements

• Main-group or representative elements
• Transition metals
• Inner transition metals

Solid, Liquid, and Gaseous Elements

• Gases: Hydrogen (H), Helium (He), Nitrogen (N), Oxygen (O), Fluorine (F), Neon (Ne), Chlorine (Cl), Argon (Ar), Krypton (Kr), Radon (Rn)
• Liquids: Bromine (Br), Mercury (Hg)
• Solids: Lithium (Li), Potassium (K), Cesium (Cs), Barium (Ba), Lutetium (Lu), Radium (Ra), Lawrencium (Lr), Lanthanum (La), Ytterbium (Yb), Actinium (Ac), Nobelium (No) and all other elements not listed as gas or liquid

Atoms

• The atom is the smallest part of the element that retains the chemical characteristics of the element itself.
• Tiny…about 10^{-10} m
  • If the atoms in your body were 1 in. in diameter, you’d bump your head on the moon.
• Huge number of atoms in even a small sample of an element
  • 1/2 carat diamond has 5 \times 10^{21} atoms…if lined up, would stretch to the sun.

Charge

• Charge is the fundamental characteristic of particles that causes electromagnetic forces.
• Some particles have charge and some do not.
• There are two types of charge, positive and negative.
• Particles with opposite charge attract.
• Particles with like charge repel.

Particles in the Atom

• Neutron (n)
  • 0 charge
  • 1.00867 u* in nucleus
• Proton (p)
  • +1 charge
  • 1.00728 u in nucleus
• Electron (e-)
  • -1 charge
  • 0.000549 u outside nucleus
• An atomic mass unit (also called the unified mass unit) is 1/12 the mass of a carbon atom that has 6 protons, 6 neutrons, and 6 electrons. The modern abbreviation for atomic mass unit is u, but amu is commonly used.

Different elements

• Different numbers of protons, neutrons, and electrons.
• Gold (Au): 79 protons, 118 neutrons, 79 electrons
• Phosphorus (P): 15 protons, 16 neutrons, 15 electrons

The Nucleus

• The protons and neutrons are in a tiny core of the atom called the nucleus.
• If an atom were the size of the earth, the diameter of the nucleus would be just a little longer than the length of a football field.
• If the nuclei of the atoms in your body were about an inch in diameter, you’d have to stand on the dark side of the earth to avoid burning your hair in the sun.

Structure of Atoms

• Electrons are strange. This will be described in more detail in a later chapter.
• For now, we will not attempt to describe the nature of the electron itself.
• We can say that it generates a negative charge that is most intense at the nucleus and diminishes in intensity with increasing distance from the nucleus.

Atomic Number and Mass Number

• The number of protons in an atom—which is also the number of electrons in an uncharged atom—is known as the element’s atomic number.
  • The atomic number can be found above each of the elements’ symbols on the periodic table.
• The sum of the numbers of protons and neutrons in the nucleus of an atom is called the atom’s mass number.

Carbon-12 Atom

• Carbon atom: 6 protons, 6 neutrons, 6 electrons
• Particle masses and charges:
  • Proton: +1 charge, 1.00728 u mass (1.6726 \times 10^{-24} g)
  • Neutron: 0 charge, 1.00867 u mass (1.6750 \times 10^{-24} g)
  • Electron: -1 charge, 0.000549 u mass (9.1096 \times 10^{-28} g)

Ions

• Ions are charged particles due to a loss or gain of electrons.
• When particles lose one or more electrons, leaving them with a positive overall charge, they become cations.
• When particles gain one or more electrons, leaving them with a negative overall charge, they become anions.

Example Ions

• Sodium:
  • Uncharged Na: 11 protons, 11 electrons
  • Na+: 11 protons, 10 electrons
• Oxygen:
  • Uncharged O: 8 protons, 8 electrons
  • O2-: 8 protons, 10 electrons

Effect on Chemical Changes

• Electrons:
  • Can be gained, lost, or shared…actively participate in chemical changes
  • Affect other atoms through their -1 charge
• Protons:
  • Affect other atoms through their +1 charge
  • Determine the number of electrons in uncharged atoms
• Neutrons:
  • No charge…no effect outside the atom and no direct effect on the number of electrons.

Isotopes

• Isotopes are atoms with the same atomic number but different mass numbers.
• Isotopes are atoms with the same number of protons and electrons in the uncharged atom but different numbers of neutrons.
• Isotopes are atoms of the same element with different masses.

Isotopes of Hydrogen

• All hydrogen atoms have 1 electron and 1 proton.
• Different isotopes have different numbers of neutrons.
  • Hydrogen-1: 0 neutrons
  • Hydrogen-2 (Deuterium): 1 neutron
  • Hydrogen-3 (Tritium): 2 neutrons

Isotopes of Tin

• Tin has ten natural isotopes:
  • Sn-112 (0.97%)
  • Sn-114 (0.65%)
  • Sn-115 (0.34%)
  • Sn-116 (14.53%)
  • Sn-117 (7.68%)
  • Sn-118 (24.23%)
  • Sn-119 (8.59%)
  • Sn-120 (32.59%)
  • Sn-122 (4.63%)
  • Sn-124 (5.79%)

Possible Discovery of Elements 113 and 115

• Dubna Joint Institute for Nuclear Research and Lawrence Livermore National Laboratory
• Bombarded a target enriched in americium (243Am) with calcium atoms (48Ca).
• From analysis of decay products, they concluded that four atoms of element 115 were created.

Why try to make elements that last such a short time?

• The technology developed to make new elements is also being used for medical purposes.
  • Heavy-ion therapy as a treatment for inoperable cancers
    • Beams of carbon atoms shot at tumor.
    • Heavier particle beam is less likely to scatter.
    • Releases most of energy at end of path so easier to focus.

To Describe Structure of Elements

• Noble gases: atoms
• Other nonmetals: molecules
• Diatomic elements: H2, N2, O2, F2, Cl2, Br2, I2
• S8, Se8, P4
• Metallic elements: cations in a sea of electrons

Description of Gas

• Particles constantly moving in straight-line paths
• About 0.1% of volume occupied by particles…99.9% empty.
• Average distance between particles is about 10 times their diameter.
• No significant attractions or repulsions.
• Constant collisions that lead to changes in direction and velocity.
• Variable volume and shape, due to lack of attractions and a great freedom of motion.

Helium Gas, He

• Each particle is a helium atom with 2 protons and 2 neutrons in a tiny nucleus, and a -2 charge cloud from 2 electrons.

Covalent Bonds and Molecules

• Covalent bond = a link between atoms due to the sharing of two electrons
• Molecule = an uncharged collection of atoms held together by covalent bonds
• The link that holds two hydrogen atoms together is a covalent bond. We call the pair of hydrogen atoms a hydrogen molecule.
• Its chemical formula is H2.

Hydrogen Molecules

• Each hydrogen atom has one electron.
• Electrons are more stable when they are paired.
• To form a pair of electrons, two hydrogen atoms combine to form one a hydrogen molecule, H2.

Hydrogen Gas, H₂

• Each particle is a diatomic molecule.

Diatomic Molecules

• Molecules that have two atoms are called diatomic.
• Hydrogen (H2), nitrogen (N2), oxygen (O2), fluorine (F2), chlorine (Cl2), bromine (Br2), and iodine (I2) are diatomic.

Bromine

• The element bromine, Br2, is composed of diatomic molecules.
• Bromine is one of the two elements that are liquids.

Description of Liquid

• Particles constantly moving.
• Up to 70% of volume occupied by particles…30% empty
• Attractions are strong but not strong enough to keep particles from moving throughout the liquid.
• Constant collisions that lead to changes in direction and velocity.
• Constant volume, due to significant attractions between the particles that keeps the particles at a constant average distance, but not constant shape, due to the freedom of motion.

Bromine Liquid, Br₂

• Each particle is a diatomic molecule.

Iodine

• Like all of the halogens (group 17), the element iodine, I2, is composed of diatomic molecules.
• Because iodine is not on our list of gases or liquids, it must be a solid at room temperature and pressure.
  • Gases - H2, N2, O2, F2, Cl2, He, Ne, Ar, Kr, and Xe
  • Liquids – Br2 and Hg
  • Solids – the rest

Description of Solid

• Particles constantly moving.
• Up to 70% of volume occupied by particles…30% empty.
• Strong attractions keep particles trapped in cage.
• Constant collisions that lead to changes in direction and velocity.
• Constant volume and shape due to strong attractions and little freedom of motion.

Iodine Solid

• Iodine is a solid at room temperature and pressure, with each particle being an I2 molecule.

Typical Metallic Solid and Its Sea of Electrons

• Atoms are packed closely together.
• Cations lie in planes.
• Electrons move freely, forming a sea of negative charge.