ATOM Chapter 14

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 LocationChargeMassOther Proton NucleusPositiveLargeSame mass as neutron Neutron NucleusNo charge (neutral) LargeSame mass as proton Electron Electron Cloud NegativeVery smallMove 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

Different Atoms

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

Isotopes of Hydrogen

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  1 st energy level: 2 electrons  2 nd energy level: 8 electrons  3 rd energy level: 8 electrons  4 th energy level: 18 electrons  5 th energy level: 18 electrons