NOTES 4 – Atomic Structure. The Idea of the Atom Democritus (~400 BC) Democritus (~400 BC) Greek philosopherGreek philosopher “All matter is made of tiny,
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NOTES 4 – Atomic StructureNOTES 4 – Atomic Structure
The Idea of the Atom The Idea of the Atom
Democritus (~400 BC)Democritus (~400 BC)• Greek philosopherGreek philosopher• ““All matter is made of tiny, All matter is made of tiny, indivisibleindivisible
particles”particles” A tomosA tomos means means unable to be dividedunable to be divided Democritus thought atoms were the Democritus thought atoms were the
smallest pieces of mattersmallest pieces of matter
The Development of the Modern The Development of the Modern Atomic ModelAtomic Model
John Dalton (1803) John Dalton (1803) • Each element has different size and Each element has different size and
shape atomsshape atoms• Atoms of different elements combine to Atoms of different elements combine to
form compoundsform compounds JJ Thompson (1897)JJ Thompson (1897)
• Atoms are solid masses of smaller Atoms are solid masses of smaller charged particles, half are positive and charged particles, half are positive and half are negativehalf are negative
The Development of the Modern The Development of the Modern Atomic ModelAtomic Model
Ernst Rutherford (1905)Ernst Rutherford (1905)• Gold Foil ExperimentGold Foil Experiment• Most of the atom is empty space Most of the atom is empty space • There is a tiny bunch of positively charged There is a tiny bunch of positively charged
particles in the center of an atomparticles in the center of an atom
The Gold Foil ExperimentThe Gold Foil Experiment
The Development of the Modern The Development of the Modern Atomic ModelAtomic Model
Niels Bohr (1911)Niels Bohr (1911)• Negatively charged Negatively charged
particles orbit the particles orbit the bunch of positively bunch of positively charged particlescharged particles
• The orbiting, The orbiting, negative particles negative particles are organized into are organized into energy levelsenergy levels
The Modern Atomic ModelThe Modern Atomic Model
The Modern Atomic ModelThe Modern Atomic Model Subatomic particlesSubatomic particles – tiny – tiny
particles that make up atomsparticles that make up atoms There are three types of subatomic There are three types of subatomic
particlesparticles::1.1. ProtonsProtons (p (p++) – positively charged ) – positively charged
particlesparticles
2.2. NeutronsNeutrons (n (n00) – particles with no ) – particles with no chargecharge
3.3. ElectronsElectrons (e (e--) – negatively charged ) – negatively charged particlesparticles
NucleusNucleus
NucleusNucleus - the dense center part of - the dense center part of the atomthe atom• Contains the Contains the protonsprotons and and neutronsneutrons• Nucleus contains 99.99% of the mass of Nucleus contains 99.99% of the mass of
an atoman atom• ElectronsElectrons orbit nucleus orbit nucleus
Atoms are extremely smallAtoms are extremely small
Comparing Subatomic ParticlesComparing Subatomic Particles
Particle Location Size & Mass Charge
Proton (p+) NucleusEqual to
NeutronPositive (+)
Neutron (n0) Nucleus Equal to Proton Neutral (0)
Electron (e-) Outside Nucleus10,000X smaller
than protons and neutron
Negative (-)
Atoms are NeutralAtoms are Neutral
Every atom has equal numbers of Every atom has equal numbers of protons (pprotons (p++) and electrons (e) and electrons (e--))
Ex. Oxygen atoms have 8 pEx. Oxygen atoms have 8 p++ and 8 e and 8 e--
The negatives cancel out the The negatives cancel out the positivespositives• 8 protons 8 protons = + 8 charge= + 8 charge• 8 electrons 8 electrons == - 8 charge- 8 charge• Total charge Total charge == 0 0
Count the protons and electrons in Count the protons and electrons in this fluorine atomthis fluorine atom
Electrons in Energy LevelsElectrons in Energy Levels
Electrons surround Electrons surround the nucleus in the nucleus in energy levelsenergy levels
The number of The number of energy levels energy levels depends on how depends on how many electrons the many electrons the atom hasatom has
How Many Electrons in Each Level?How Many Electrons in Each Level?
11stst energy level holds 2 e energy level holds 2 e--
22ndnd energy level holds up to 8 e energy level holds up to 8 e--
33rdrd energy level holds up to 18 e energy level holds up to 18 e--
Atoms with 2 eAtoms with 2 e- - or less have 1 energy or less have 1 energy levellevel
Atoms with 3 to 10 eAtoms with 3 to 10 e- - have 2 energy levelshave 2 energy levels Atoms with more than 10 eAtoms with more than 10 e- - have at least have at least
3 energy levels3 energy levels
Valence ElectronsValence Electrons
Valence electronsValence electrons - The electrons in the - The electrons in the outer most energy level outer most energy level
Valence electrons determine the Valence electrons determine the reactivityreactivity of an atom of an atom • Will it bond with other atoms?Will it bond with other atoms?
Ex. Oxygen atoms have 8 electronsEx. Oxygen atoms have 8 electrons• 2 in the first level2 in the first level• 6 in the second level6 in the second level• How many valence e- does an oxygen atom How many valence e- does an oxygen atom
have?have? 66
The periodic table gives information The periodic table gives information about 1 atom of any elementabout 1 atom of any element
The periodic table gives information The periodic table gives information about 1 atom of any elementabout 1 atom of any element
The periodic table gives information The periodic table gives information about 1 atom of any elementabout 1 atom of any element
The periodic table gives information The periodic table gives information about 1 atom of any elementabout 1 atom of any element
The periodic table gives information The periodic table gives information about 1 atom of any elementabout 1 atom of any element
The periodic table gives information The periodic table gives information about 1 atom of any elementabout 1 atom of any element
Atomic NumberAtomic Number = Number of protons & = Number of protons & electronselectrons• Ex. 1 oxygen atom has 8 protons and 8 electronsEx. 1 oxygen atom has 8 protons and 8 electrons
Mass NumberMass Number = Number of protons + neutrons = Number of protons + neutrons• Ex. 1 oxygen atom has 16 protons + neutronsEx. 1 oxygen atom has 16 protons + neutrons• To figure out the # of neutrons, subtract the atomic To figure out the # of neutrons, subtract the atomic
number from the mass numbernumber from the mass number• 16 – 8 = 8 so an oxygen atom has 8 neutrons16 – 8 = 8 so an oxygen atom has 8 neutrons
How many protons, neutrons, and electrons How many protons, neutrons, and electrons are in one atom of sodium?are in one atom of sodium?
Atomic number is Atomic number is 11, so there are:11, so there are:• 11 protons11 protons• 11 electrons11 electrons
Mass number is 23, Mass number is 23, so there are:so there are:• 23 – 11 = 1223 – 11 = 12• 12 neutrons12 neutrons
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