Atomic Structure

The smallest pieces of matter…Atom

the tiny building block of all matters whether a solid matter , a liquid matter or gaseous matter. These atoms are the smallest particles of a chemical element that still exhibit all the chemical properties unique to that element. There are 92 known natural elements that exist. comes from Greek word “atomos” meaning “not divisible”

• The atom:– The basic building block of matter

• There are 90 naturally occurring kinds of atoms– Scientists in labs have been able to make about 25 more

• Around 1900, people thought of atoms as permeable balls with bits of electric charge bouncing around inside

• People soon realized that they could could categorize atoms into groups that shared similiar chemical properties (as in the Periodic Table of the Elements). This indicated that atoms were made up of simpler building blocks, and that it was these simpler building blocks in different combinations that determined which atoms had which chemical properties.

Subatomic Particles

POSIT IVECHARGE

PROT ONS

NEUT RALCHARG E

NEUTRONS

NUCLEUS

NEG ATIVE CHARG E

ELECTRONS

AT OM

Most of the atom’s mass.

NUCLEUS ELECTRONS

PROTONS NEUTRONS NEGATIVE CHARGE

POSITIVE CHARGE

NEUTRAL CHARGE

ATOM

QUARKSAtomic Numberequals the # of...

equal in a neutral atom

Atoms Classifying the composition of objects at the atomic level is now a familiar process.

This ring, for example, is made up of only 2 kinds of atoms: gold (Au) and Carbon (C)

• Chemical Compounds formed when atoms react with each other. combination of elements

• Molecule smallest part of a compound that can exist independently

Periodic tableThe periodic table lists about 114 atoms with distinct properties: mass, crystal structure, melting point…

The range and pattern of properties reflects theinternal structure of the atoms themselves.

Atomic Structure• Atoms are composed of 2 regions:

– Nucleus: the center of the atom that contains the mass of the atom

– Electron cloud: region that surrounds the nucleus that contains most of the space in the atom

NucleusElectronCloud

What’s in the Nucleus?• The nucleus contains 2 of the 3

subatomic particles:– Protons: positively charged

subatomic particles– Neutrons: neutrally charged

subatomic particles

• Electrons negative charge was discovered by Sir Joseph Thomson in April 30, 1847 electric charge of -1.602 x 10-19 C and mass of 9.109 x 10-31 kg

• Protons positive charge was discovered by Ernest Rutherford in 1919 electric charge of 1.602 x 10-19 C and mass of 1.6726 x 10-27 kg

• Neutrons no charge was discovered by Sir James Chadwick in 1932 no electric charge and mass of 1.6749 x 10-27 kg

Subatomic Particles

How do these particles interact?

• Protons and neutrons live compacted in the tiny positively charged nucleus accounting for most of the mass of the atom

• The negatively charged electrons are small and have a relatively small mass but occupy a large volume of space outside the nucleus

How do the subatomic particles balance each other?• In an atom:

– The protons = the electrons• If 20 protons are present in an atom then 20

electrons are there to balance the overall charge of the atom—atoms are neutral

– The neutrons have no charge; therefore they do not have to equal the number of protons or electrons

– Isotopes – elements that exist in different forms differing in the number of neutrons

How do we know the number of subatomic particles in an

atom?• Atomic number: this number indicates the number of protons in an atom– Ex: Hydrogen’s atomic number is 1

• So hydrogen has 1 proton– Ex: Carbon’s atomic number is 6

• So carbon has 6 protons**The number of protons identifies the

atom. Ex. 2 protons = He, 29 protons = Cu

• Mass number: the number of protons and neutrons in the nucleus– Ex: hydrogen can have a mass of 3. Since it has 1 proton it must have 2

neutrons

– # of neutrons = mass # - atomic #

How do we know the number of subatomic particles in an

atom?

Determining the number of protons and neutrons

• Li has a mass number of 7 and an atomic number of 3– Protons = 3 (same as atomic #)– Neutrons= 7-3 = 4 (mass # - atomic #)

• Ne has a mass number of 20 and an atomic number of 10– Protons = 10– Neutrons = 20 - 10= 10

What about the electrons?• The electrons are equal to the

number of protons– So e- = p = atomic #

• Ex: He has a mass # of 4 and an atomic # of 2– p+ = 2– no = 2– e- = 2

Determine the number of subatomic particles in the

following:

• Cl has a mass # of 35 and an atomic # of 17– p+ = 17, no = 18, e- = 17

• K has a mass # of 39 and an atomic # of 19– P+ = 19, no = 20 e- = 19

How exactly are the particles arranged?

• Bohr Model of the atom:Reviewers think this could lead to misconceptions! All of the

protons and the neutronsThe 1st ring can hold up to 2 e-The 2nd

ring can hold up to 8 e-

The 3rd ring can hold up to 18 e-The 4th ring and any after can hold up to 32 e-

Bohr’s Model

n Shell Number of electons (2n2)

1 K 2

2 L 8

3 M 18

What does carbon look like?

Mass # = 12 atomic # = 6

p+ = 6 no = 6 e- = 6

6 p and 6 n live in the nucleus

Inside Atoms: neutrons, protons, electrons

Carbon (C )

Gold (Au)Atomic number Z=6 (number of protons)

Mass number A=12 (number of protons + neutrons)

# electrons = # protons (atom is electrically neutral)

Atomic number Z = 79

Mass number A = 197

#electrons = # protons

Properties of nucleons

• Units: – The electric charge of an electron is -1 in these units.– Mass units are “billion electron volts” where 1 eV is a typical

energy spacing of atomic electron energy levels.

Name Mass Electric Charge

Proton 1 GeV +1

Neutron 1+ GeV 0

Ions• An atom with a net charge

– Anion negatively charged ion– Cation positively charged ion

Quarks

substructures of protons and neutrons (nucleons)

discovered in 1968 at Jefferson Lab

Flavors of QuarksFlavor Symbol Charge

Up U +2/3

Down D -1/3

Charm C +2/3

Strange S -1/3

Top T +2/3

Bottom B -1/3

The Quantum Model The Quantum Model Physicists have developed a theory called The Quantum

Model that explains what the world is and what holds it together. It is a simple and comprehensive theory that explains all the hundreds of particles and complex interactions with only: • 6 quarks- up/down, charm/strange, and top/bottom

• Compose protons and neutrons• 6 leptons- The best-known lepton is the electron. • Force carrier particles- like the photon.

All the known matter particles are composites of quarks and leptons, and they interact by exchanging force carrier particles.

He

Quantum Particles Quantum Particles Example:

• Protons have two up and one down quark.• Neutrons have two down and one up quark.

Atom Builder activity

Further layers of substructure:

If each proton were 10 cm across, each quark would be .1 mm in size and the whole atom would be 10 km wide.

www.cpepweb.org

u quark: electric charge = 2/3

d quark: electric charge = -1/3

Proton = uud electric charge = 1

Neutron = udd electric charge = 0