Atoms and the Periodic Table

Sign on to clickers!!!

Atom: the smallest particle of an element. Everything is made of atoms

Proton: positive particle in the nucleus

Neutron: neutral particle in the nucleus

Electron: tiny negative charge outside the nucleus

Atoms are mostly….

… empty space!

Element: a substance made of only one kind of atom, cannot be chemically or physically separated into other substances.

Atomic number: the number of protons in an atom. All elements are identified by their atomic number.

For example, any element with 6 protons is Carbon, regardless of how many neutrons (or electrons) it has

Atomic mass: the total mass of all the protons, neutrons and electrons in an individual atom.

Since electrons have so little mass, the atomic mass is approximately equal to the sum of the number of protons and neutrons- the nucleons.

Molecule: Two or more ATOMS bonded together.

Examples:

Water = H2O

Oxygen = O2

Compound:Two or more different ELEMENTS bonded together.

Homogenous mixture: substances are evenly distributed so that one part of the mixture can’t be distinguished from another.

Example: stirring cream into your coffee

heterogenous mixture: substances are not evenly distributed and can be distinguished from another.

Example: soil, oil and vinegar

Ion: an atom or molecule that has a positive or negative electric charge because its number of protons is not equal to its number of electrons.

Ions will NOT have a net charge of zero, but will be either positive or negative

Isotope: Atoms that have the same number of protons but different number of neutrons. They are the SAME element!

Notation that indicates nucleon number(approx = atomic mass) as well as atomic number

He42

C146

C126

Atomic number = protons

Number of nucleons= protons + neutronsApprox. atomic mass

This is “Carbon-14”. How many neutrons does it have?

This is “Carbon-12”. How many neutrons does it have?

Carbon-14 and Carbon-12 are different ????? of Carbon.

Chemical Formula: A description that uses numbers and symbols of elements to describe a molecule.

H2ONaClCaCl2

Periodic Table: A chart that lists the elements by atomic number and electron arrangement.

Radioactive Elements

Some elements are unstable, especially if they’re really massive, and spontaneously fall apart or decay and thereby lose energy.

Why would nucleii tend to fall apart?? (Think about what protons do to each other)

These unstable elements are called RADIOACTIVE.

All elements with more than 83 protons are RADIOACTIVE.

Radioactive decay transforms the atom’s nucleus so that it is either in a different state of energy or it has different nucleons (transmutation) and is therefore a different element. Transmutation:

Radioactive Elements

They will continue to decay until they are stable (non-radioactive), even if it takes years.

The amount of time it takes until half of the atoms in a radioactive sample have decayed is called its

HALF-LIFE.

The individual rows are called Periods.The individual columns are called GroupsElements in the same group have the same number of valence electrons and will react, bond, behave, in similar ways.

Metals Non metals

How to remember??In the alphabet……

“M” comes before “N”

Metals have “free electrons” (in their outer shell) that’s how they conduct electricityMetals can DONATE those electronsNonmetals can ACCEPT those electrons.Group 1 donates 1, Group 2 donates 2, etc.Group 17 (VIIA) accepts 1, Group 16 accepts 2, etc.Think of those electrons flowing like electricity flows from the metals over to the nonmetals

e-

The ability to accept electrons is called electronegativity.

Which elements MOST readily accept electrons?

The group of elements that only need ONE more electron to fill their outermost shell.

Group 17 is called the Halogens.And, in this group, the element Fluorine has the highest “electronegativity” – the ability

to accept electrons

A Halide is a binary compound of which one part is a halogen.

Examples: KCl and AgBr

Acids and Bases

pH scale identifies acids and bases with a number:

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Acids Neutral Bases

How to remember???

In the alphabet, “A” is before “B”

Basic substances will turn litmus paper BLUE

Acidic substances will turn litmus paper RED.

Examples of acids: hydrochloric acid, lemon juice, vinegar

Examples of bases: ammonia, soap, baking soda (often bases are slippery stuff!)

How do you know if it’s an acid or base? (acidity or alkalinity)

Acids have H+

Bases very often have OH-

(“hydroxide”)

How to remember???In the alphabet, “H” comes before

“O”, just like “acids” come before “bases

Water

Think of water as an H+ bonded with an OH-.

H2O (two hydrogen, one oxygen)

Equal acid and base. Therefore….

Pure water is neutral with a pH of

7

Which is one reason water is very important…

Some things dissolve better in acids.

Some things dissolve better in bases.

Water is a universal solvent.

O

H

H

Acid, H+Base, OH-

Rather like the Earth has a North Pole and a South Pole, water is POLAR, with a more “acid / +” pole and

a more “base / -” pole. That’s why it’s called a UNIVERSAL SOLVENT.

This is how water easily breaks apart ionic compounds. It surrounds both negative and positive ions and breaks apart ionic solids.

Physical vs Chemical Changes

Ice melting

Iron rusting

Food digesting in your stomach

Wood burning

Body decomposing

Sugar dissolving

Which of these describes a pollution-producing process that involves only a physical change?

a) Coal with a high sulfur content is burned, producing gases that cause acid rain.

b) Chlorofluorocarbons are released, changing ozone in the upper atmosphere into oxygen.

c) Hot wastewater is discharged into a lake.

d) Nitrogen oxide emissions combine with water vapor, producing nitric acid.

The correct answer is “c”

Solubility of a solid in a liquida measure of how much solute will dissolve

into the solvent

Temperature will affect solubility- the solubility will be INCREASED as the temperature is increased.

Stirring will increase solubility.Molecular or Particle Size will affect the

solubility. The larger the molecule or particle the less soluble the substance will be. So smashing something into smaller pieces makes it dissolve better.

Solubility of a gas in a liquidThink of carbonation in your soft

drink!Pressure will affect solubility of a gas in a liquid. As the outside pressure goes up, the solubility (staying dissolved) will go up. For example: the CO2 (fizzies) stays dissolved in your coke because it’s bottled under high pressure. Once you open the lid, the bubbles began to escape. Higher pressure increases solubility.

Temperature affects the solubility. Cokes lose their fizziness faster as the temperature increases.Colder temperature increases solubility.

Decompression sickness can happen in these situations:

-A diver ascends too quickly from a dive -An unpressurized aircraft goes too high. -The cabin pressurization system of a high-flying aircraft

fails. -Divers flying in any aircraft shortly after diving. -An astronaut exits a space vehicle to perform a space-

walk.

These situations cause inert gases, generally nitrogen, which are normally dissolved in body fluids and tissues, to come out of physical solution (“outgas”) and form gas bubbles.

If nitrogen is forced to come out of solution too quickly, bubbles form in parts of the body causing the signs and symptoms of the "bends" which can be itching skin and rashes, joint pain, sensory system failure, paralysis, and death.

As a scuba diver goes deeper underwater, the diver must be aware that the increased pressure affects the human body by increasing the-

a) body’s temperature

b) Amount of dissolved gases in the body

c) Amount of suspended solids in the body

d) Concentration of minerals in the body

The correct answer is “b”

All of these can affect the rate at which a solid dissolves in water except

A) Decreasing air pressure

B) Stirring the water

C) Increasing the temperature of the water

D) Using larger crystals of the solid

The correct answer is A, decreasing the pressure in the air above the water won’t affect the rate the solid dissolves

As the pressure increases,A. the solubility of a gas in a liquid

increases.B. the solubility of a gas in a liquid

decreases.C. the solubility of a solid in a liquid

increases.D. the solubility of a solid in a liquid

decreases.

Ionic Bonds

Atoms will bond together in order to have a stable valence shell.

One atom may give up an electron to another atom so that they both have stable valence shells. Since one atom lost an electron and the other gained an electron, they are both now IONS.

This called an ionic bond.

36

Ionic BondsFor TAKS, you must know how to write the

chemical formula after the ionic bond has formed.

Example: what is the chemical formula for Aluminum Hydroxide formed when

Al+3 is bonded with OH- ?

Just “cross-multiple” the numbers!

Al(OH)3

Let’s try some:

Zn2+ and Cl

ZnCl2Al3+

and SO42-

Al2(SO4)3

Ca1+ and CO31-

CaCO3

Fe3+ and SO42-

Fe2(SO4)3

NH4+ and PO4

3-

(NH4)3PO4

Conservation of Mass

According to the law of conservation of mass in a closed system, the total mass of the reactants before a reaction is equal to the total mass of the products after the reaction.

Total mass before = total mass after

Conservation of Mass

For example: In this reaction, how much zinc was present in the zinc carbonate?

64 g Calcium + 192 g Zinc Carbonate 152 g Calcium carbonate + ?? g Zinc

Think of the as an =

64 + 192 = 152 + ??There was 104 g of Zinc

3 g of CaCl2 reacted with 2 g of Na3PO4

the products were 1 g of Ca3(PO4)2 and table salt- NaCl.

How many grams of NaCl were produced?

In a similar way, there is the same number of atoms of each element before a chemical reaction as there is after the reaction.

# of atoms of each element before a reaction

=

# of atoms of each element after a reaction

That’s where balancing equations is important.

Density

One characteristic of matter is DENSITY

Density = mass / volume

Unit: kg / m3 or g / cm3

The density of water is 1000 kg / m3

Or 1 g / cm3

An object will float in a liquid if its density is less than that of the liquid.

Buoyancy-Archimedes Principle

An object immersed in a fluid is buoyed up with a force that is equal to the weight of the displaced fluid.

That’s why you seem to weigh less in a swimming pool that you actually do!

Apparent Weight = Actual Weight – Buoyant Force

In this example, the stone weighs 48 N out of water and 38 N submerged in

water.What was the buoyant force?

How much did the displaced water weigh?

Buoyant Force = Weight of displaced fluid

But buoyancy applies to air as well as water!It is what gives a lifting force to hot air balloons.

The weight of the air displaced to make room for the balloon is pushing upward on the balloon!

Archimedes' Principle explains why steel ships float when solid steel spheres do not float. Because of all the air in the hull, the overall

density is less than that of water, therefore, it floats- the buoyant force equals the weight

as the ship floats on the surface of the ocean.

Fluids in Motion

Fluids include both liquids and gases.

Viscosity: the resistance to flow

Honey is more viscous than water.