04/19/23 4.2 The Structure of an Atom 1

4.2 THE STRUCTURE OF AN ATOM VOCABULARY:

proton electron neutron

OBJECTIVES: Identify three subatomic particles & compare

their properties.

Distinguish the atomic number of an element from the mass number of an isotope, and use these numbers to describe the structure of an atom.

VOCABULARY: atomic number mass number isotope

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PROPERTIES OF SUBATOMIC PARTICLES By 1920,

evidence for existence of 2 subatomic particles (+ & - charges)

Rutherford predicted existence of 3rd particle

subatomic particles:

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COMPARING SUBATOMIC PARTICLES distinguished by mass, charge, & location

e- charge = in size to, but opposite of, charge of p+

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PROPERTIES OF SUBATOMIC PARTICLES: ELECTRONS negatively (-) charged particles Thomson detected were later named electrons

Electron symbol: e- charge: negatively charged (1-) location: in space outside of nucleus

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Rutherford also concluded that amount of positive (+) charge varies among elements

Proton symbol: p+

charge: positively charged (1+) location: in nucleus of atom

PROPERTIES OF SUBATOMIC PARTICLES: PROTONS

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PROPERTIES OF SUBATOMIC PARTICLES: NEUTRONS Discovered in 1932, by English physicist James Chadwick

designed experiment to show that neutrons exist

concluded that particles he produced were neutral b/c a charged object did not deflect their paths

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PROPERTIES OF SUBATOMIC PARTICLES: NEUTRONSNeutron

symbol: ncharge: neutral (0)location: in nucleus of atom

Hey Bartender! How much for a

soda?

For you… No charge.

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Proton:

Neutron:

Electron:

• Heavy, Positive

• Heavy, Neutral

• Light, Negative

SUBATOMIC PARTICLES

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COMPARING SUBATOMIC PARTICLES

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COMPARING SUBATOMIC PARTICLES everything known about nucleus &

subatomic particles based on how particles behave

Currently, don’t have instrument to show inside of atom, but do have microscopes that show how atoms are arranged on a material’s surface (Page 111)

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ATOMIC NUMBER Atomic number of an element equals the

number of protons in an atom of that element.

i.e. 1 proton in nucleus of every hydrogen atom. Therefore, atomic number of hydrogen = 1.

Atoms of different elements have different number of protons.

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ATOMIC NUMBER

atoms are neutral each + charge in an atom is

balanced by a - charge.

Therefore atomic # of an element also equals # of electrons in an atom.

How many electrons does a hydrogen atom have?

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MASS NUMBER

Mass number - sum of the protons and neutrons in the nucleus of an atom.

i.e. in an atom of aluminum there are 13 protons & 14 neutrons. What is the mass number?

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MASS NUMBER

Mass number - sum of the protons and neutrons in the nucleus of an atom.

i.e. in an atom of aluminum there are 13 protons & 14 neutrons. What is the mass number?

13 protons + 14 neutrons = 27

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MASS NUMBER http://web.visionlearning.com/custom/

chemistry/animations/CHE1.3-an-animations.shtml

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MASS NUMBER

If you were given the mass number and atomic number of an atom, how can you find the number of neutrons?

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MASS NUMBER

If you were given the mass number and atomic number of an atom, how can you find the number of neutrons?

Answer: by subtracting atomic # from mass #

# of neutrons = mass # – atomic #

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ISOTOPES

Dalton’s atomic theory: all atoms of a given element are identical

Every atom of a given element DOES have same # of protons & electrons but does not have same # of

neutrons.

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ISOTOPES Isotopes - atoms of the same element that have different numbers of neutrons and different mass numbers.

Therefore, isotopes of an element have the same atomic number but different mass numbers because they have different numbers of neutrons.

representation of two isotopes of carbon

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ISOTOPES

Hydrogen atoms: all have 1 proton most have no neutrons and mass #

of 1 (hydrogen 1) some have 1 neutron (hydrogen 2)

or 2 neutrons (hydrogen 3)

http://web.visionlearning.com/custom/chemistry/animations/CHE1.3-an-

isotopes.shtml http://web.visionlearning.com/custom/chemistry/overheads/CHE1.3-oh-

isotopes.shtml

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ISOTOPES

All oxygen atoms have 8 protons. How many neutrons are in an atom of oxygen 18?

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ISOTOPES

All oxygen atoms have 8 protons. How many neutrons are in an atom of oxygen 18?

Answer: # of neutrons = mass # – atomic # mass # = 18 atomic # = 8 # of neutrons = 18 – 8 = 10

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ISOTOPES http://www.brainpop.com/science/

matterandchemistry/isotopes/

http://www.brainpop.com/science/matterandchemistry/atoms/