Atomic Structure

Unit I

Atomic StructureAtoms are composed of 2 regions:

Nucleus: the center of the atom that contains the mass of the atomElectron cloud: region that surrounds the nucleus that contains most of the space in the atom

d

What’s in the Nucleus?• TThe nucleus

contains 2 of the 3 subatomic particles:• Protons:(p+) positively charged subatomic particles• Neutrons:(no) neutrally charged subatomic particles

• The number of neutrons can change.

What’s in the Electron Cloud?

• The 3rd subatomic particle resides outside of the nucleus in the electron cloud• Electron:(e-) the

subatomic particle with a negative charge and relatively no mass

and

How do these particles interact?

• Protons and neutrons are compacted in nucleus.

• They accounts for most of the mass of the atom.

• The negatively charged electrons are small and have small mass but occupy a large volume (space) outside the nucleus.

How do the subatomic particles balance each other?

• In an atom:• The #of protons = # of the electrons• If 20 protons than 20 electrons are to balance the overall charge of the atom

• The neutrons have no charge; •Neutrons do not equal the number of protons or electrons

• Mass number(A) = the number of protons + neutrons in the nucleus.

• Atomic number(Z): indicates the number of protons in an atom

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How do we know the number of subatomic particles in an atom?

A Z

Determining the number of protons and neutrons

Neutrons=(mass # - atomic #)= A - Z

Ex: 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(Helium) has a mass # of 4 and an atomic # of 2• p+ = 2• no = 2• e- = 2

Number Protons + Number of neutrons

Determine the number of subatomic particles in the

following:• Cl has a mass # of 35 and an atomic # of

17

• K has a mass # of 39 and an atomic # of 19

p+ = 17, no = 18, e- = 17 (35-17=18)

P+ = 19, no = 20 e- = 19 (39-19=20)

Rutherford’s Model He discovered the nucleus and proposed that an atom is just

like a miniature solar system, with electrons orbiting around a massive nucleus, and as mostly empty space, with the nucleus occupying only a very small part of the atom.

The 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-

Energy Levels of an AtomNumber of Electrons in each level.

Valence Electrons

VALENCE ELECTRONSWhy are they important?

VALENCE ELECTRONS ARE RESPONSIBLE FOR FORMING BONDS BETWEEN ATOMS DURING A REACTION.

Types of bondingBONDS form when two or more atoms react together or when atoms try to reach stability. ATOMS will share valence electrons or exchange(give or take) valence electrons to make bonds:Covalent (Molecular) Bonds: Share electronsIonic Bonds: One atom will give and the other will take an electronMetallic Bonds: Electron sharing within a metal. It is b/c of electrostatic forces.

IsotopesA

Atoms that have the same protons and electrons but different number of neutrons. It will change the mass number of the atom. Ex: 3 Isotopes of Hydrogen

Hypothesis, Theory, Or Law?Hypothesis must be testable, repeatable, and

relate to observation. PREDICT EVENT.– If – then – because statements

Theory – based on observation, experimentation and reasoning– Never completely proven, but modified

continually.EXPLAINS EVENTLaw – expression that reliably describes behavior

of natural world. DESCRIBES EVENT