Chapter 17 - Atomic Structure

•Scientists have developed their own shorthand for dealing with long, complicated names.

•Chemical symbols

consist of one capital

letter or a capital letter

plus one or two smaller

letters.

Scientific Shorthand

•Capitals matter!•Element symbols contain ONE capital letter followed by lowercase letter(s) if necessary. •Scientists use two letters for some elements because there are more elements than letters.

Metals that form

Bright blue Co vs. CO Poisonous Gas

Solid compounds

Chemical Symbols

•An element is matter that is composed of one type of atom, which is the smallest piece of matter that still retains the property of the element.

•Atoms are composed of particles called protons, neutrons, and electrons

HOW DO WE KNOW THIS?

Atomic Components

Studying Atoms1. Ancient Greek Models of Atoms

– 400 BC– Greek Philosopher Democritus- named

atoms(atomos)– Believed that all matter consisted of small

particles that could not be divided and were impossible to destroy.

– He called these particles atoms.

2. Dalton’s Atomic Theory – still use parts of this

– John Dalton – 1803• All elements are composed of atoms• Atoms of the same element are alike, atoms of

different elements are different• Compounds are formed by joining two or more of

these elements in a set ratio

Atoms of the same element Atoms of different elements

3. Plum Pudding Model– JJ Thomson – 1897- Plum Pudding

• Most of the atom was positively charged• Atoms had negative charges embedded in pos.

charged material

4. Rutherford’s Model– Ernest Rutherford – 1911- gold foil experiment -

nucleus• Gold Foil Experiment – Rutherford fired positively

charged particles at a sheet of gold foil. Most passed through.(like charges repel)

• Rutherford discovered the nucleus as a result of his experiment

5. Bohr Model– Neils Bohr – 1913

• Worked with Rutherford• Electrons move in definite orbits• “Orbits” are referred to as energy levels

Modern Atomic Theory• Energy levels – the possible energies that

electrons can have

• Electrons cannot exist between energy levels

• Electrons can move from one energy level to another.– when an atom gainsgains (moves up) – losesloses energy (falls to a lower level)

Electrons Losing EnergyElectrons Losing Energy• When an electron loses energy, it emits

light.

• Each element has a specific wavelength and frequency at which the light is emitted.

• This gives each element a unique color.– Example: Copper Chloride–

Sodium Chloride–

Potassium Chloride–

• We can see this through flame tests

6. Electron Cloud Model – current Atomic Model

• Electron cloud is a visual model of the most likely locations and motions of electrons in atoms.

The electron cloud is a visual model of the probable locations of electrons in an atom. The probability of finding an electron is higher in the denser regions of the cloud.

The Structure of the Atom

• Atoms consist of subatomic particles– Protons

• Positive charge• Located in the nucleus

– Neutrons• No charge• Located in the nucleus

– Electrons• Negative charge• Located in the electron cloud

Subatomic Particles

•Protons and neutrons are made up of smaller particles called quarks.

•So far, scientists have confirmed the existence of six uniquely different quarks

Quarks—Even Smaller Particles

•Scientists theorize that an arrangement of three quarks held together with the strong nuclear force produces a proton.

•A different arrangement of three quarks produces a neutron

1. up 5. top2. down 6. bottom3. charm

4. strange

Quarks

He

•To study quarks, scientists accelerate charge particles to tremendous speeds and then force them to collide with—or smash into—protons. This collision causes the proton to break apart.

•The particles that result from the collision can be detected by various collection devises.

•Atom smashers

Finding Quarks

Atomic Number and Mass Number

• Atomic Number – Identifies the element– # of protons in the nucleus of an atom– Different elements have different numbers of

protons– When this number changes, you get a

different element.

• Mass Number– Sum of an atoms protons and neutrons– Number of neutrons = mass # - Atomic #

Isotopes

• Isotopes are atoms of the same element with different numbers of neutrons and different mass numbers.

This can also be written in Hyphen Notation Carbon - 12

Nuclear Notation

Average Atomic Mass

• The atomic mass that is on the periodic table, is a weighted average of all of the isotopes of a given element.

• The more abundant an isotope is, the more heavily it counts towards the average atomic mass.

• Example: Calculate

the average atomic

Mass.

Mass number Abundance

Si-28 92.21 %

Si-29 4.70 %

Si-30 3.09 %

Atomic Orbitals

• Orbital is a region of space around the nucleus where an electron is likely to be found.