I CAN IDENTIFY THE PROPERTIES OF THE THREE SUBATOMIC PARTICLES OF ATOMS.
I CAN USE A MODEL TO REPRESENT THE STRUCTURE OF AN ATOM AND IDENTIFY THE FORCES THAT HOLD THE SUBATOMIC PARTICLES TOGETHER.
I CAN IDENTIFY THE NUMBER OF SUBATOMIC PARTICLES BASED ON THE PERIODIC TABLE OF ELEMENTS.
Competency G – Properties of Matter
Electric Charge
Electric Charge is a property of matter 2 types of Electric Charge: positive or
negative Electric Charge holds atoms together Opposite charges ATTRACT Same charges REPEL
Electric Charge
Matter is electrically neutral when positive and negative charges are EQUAL and total electric charge is ZERO
History of the Atom
Important Discoveries: 1. J.J. Thomson (1897) discovered electrons He passed electricity through a gas and
noticed smaller negatively charges particles were given off
He proposed negative electrons were sprinkled throughout positively charged atom
History of Atom
2. Rutherford, Geiger and Marsden (1911) discovered atom was mostly empty space with dense core called nucleus Gold Foil experiment –
most atoms passed through gold foil
Atomic Structure
Subatomic
Particles
Location
Charge Mass Other
Proton Nucleus Positive Large Same mass as neutron
Neutron
Nucleus No charge
(neutral)
Large Same mass as proton
Electron
Electron Cloud
Negative Very small
Move very fast
Atomic Structure
Protons and Neutrons are massive compared to electrons
Mass of nucleus determines mass of atom
99% of atom’s mass in nucleus where protons and neutrons are located
Electron cloud is empty space around the nucleus
Electron cloud is 10,000 larger than nucleus – reason why atom is mostly empty space
Forces inside Atoms
Electromagnetic Force: Attractive force between electrons (-) and protons (+) binding electrons to nucleus
Forces inside Atoms
Strong nuclear force: force that holds nucleus together Very strong Attracts neutrons and protons to each other Works at only extremely small distances
Forces inside Atoms
Weak Force: force that will turn a single neutron outside the nucleus into a proton and electron Weaker than electromagnetic force and
strong nuclear force Important when atoms break apart
Forces inside Atoms
Gravity: force of gravity inside atoms is very weak because an atom does not have a large mass
How to tell Different elements apart?
Different elements contain DIFFERENT numbers of protons
Atomic Number: number of protons
All atoms of same element have same number of protons in nucleus
Each element has unique atomic number
Stable Atoms
Stable atoms are neutral atoms In STABLE atom number of protons
EQUALS number of electrons
PROBLEM SOLVING
What is the atomic number of Helium? How many protons are in Helium? How many electrons are in Helium
What is the atomic number of Carbon? How many protons are in Carbon? How many electrons are in Carbon?
Ions
Ions: atoms that have different numbers of protons than electrons
Ions have an electric charge Positive charged ions: contain more
protons Negative charged ions: contain more
electrons
Isotopes
Isotopes: atoms of the same element that have different numbers of neutrons
Mass number: number of protons + number of neutrons Represents everything in nucleus
Number of neutrons = mass number – atomic number
Referring to Atoms
When referring to atoms, most scientists write the name of the atom and then the mass number of the atom
Example: Nitrogen - 14 or Nitrogen – 15 Both have the SAME number or protons Both have the SAME number of electrons They have DIFFERENT numbers of neutrons
Isotope Notation
For Isotope Notation, scientists write the symbol of the element
Superscripted next to the symbol is the mass number
Subscripted next to the symbol is the atomic number
PROBLEM SOLVING
How many neutrons are present in an aluminum atom that has an atomic number of 13 and a mass number of 27?
Radioactivity
Most elements have stable isotopes Stable means nucleus stays
together Radioactive means nucleus is
unstable and breaks apart because too many or too few neutrons
Radioactive isotope eventually changes into stable isotope
Radioactivity is a process in which the nucleus spontaneously emits particles as it changes into a more stable isotope
Radioactivity
Radioactivity can change one element into a completely different element
Alpha Decay: when nucleus ejects 2 protons and 2 neutrons Atomic number decreases by 2 Mass Number decreases by 4
Beta Decay: when a neutron splits into a proton and electron Atomic number increases by 1 Mass Number stays the same
Gamma Decay: How a nucleus gets rid of excess energy Nucleus gives off gamma rays Atomic Number and Mass Number stay the same
Electrons – 14.2
Atoms interact with each other through electrons
Example: Chemical bonds involve only electrons
Light Spectrum
Almost all light you see comes from atoms
Spectrum: is a specific pattern of colors given off by an element
Spectrum includes very specific colors or characteristics
Spectral line: individual color in a spectrum
Spectroscope: instrument that separates light into a spectrum
Light
Energy level: allowed energies for electrons
Electrons must be in one energy level or another – not between levels
Electrons change energy levels by absorbing or emitting light
Light is given off when an electron moves from a higher energy level to a lower energy level
Bohr Model
Neils Bohr: Danish physicist who proposed concept of energy levels
When an electron moves from a higher energy level to a lower one, the atom gives up the energy difference between the two levels
The energy comes out as different colors of light
Electrons and Energy Levels
Electrons located in the Electron Cloud
Electron Cloud divided into energy levels
Electrons farther from the nucleus have more energy
Energy Levels
Rules for energy levels: 1. energy of electron has to match 1
of the energy levels 2. each energy level can hold a
certain number of electrons 3. when electrons are added to an
atom, fill lowest empty energy levels first
Energy Levels
1st energy level: 2 electrons 2nd energy level: 8
electrons 3rd energy level: 8
electrons 4th energy level: 18
electrons 5th energy level: 18
electrons