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The Structure of Atoms The Structure of Atoms andand

IonsIons

Mr. Shields Regents Chemistry U01 L03

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Atomic NumberAtomic Number

1. The number of protons an element has determines it’s ATOMIC NUMBER

Every element has a unique atomic #

2. Therefore every element has a different number of protons

This makes it different from every other

element

Mosley’s and Rutherford’s work explained the key role of Protons in defining an element.

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Atomic NumberAtomic Number

When we write the atomic number it is written to the Left of the element symbol and at the bottom.

Atomic no. 3

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Mass NumberMass Number

An Atoms Mass Number is the sum of both Protons & Neutrons in the nucleus.

Protons and neutrons have about the same mass

For example Carbon’s Atomic No. = 6.

So if Carbon also had 8 Neutrons it’s Mass Number would be?

6p + 8n = 14

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Mass NumberMass NumberWhen we write the Mass Number it is written to the Left of the element symbol and at the top.

Atomic MassNumber = 7

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Atomic ChargeAtomic Charge

If atoms are neutral but have Positive Protons In the nucleus then there must be one electron to balance the positive charge of each ProtonTherefore the ATOMIC NUMBER not only indicates

the number of PROTONS but ALSO the number of ELECTRONS

+/-

We know atoms must be electrically neutral. Why?

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NotationNotation

1212CC66

12 = no. of protons + neutrons.12 = no. of protons + neutrons. 6 = no. of protons.6 = no. of protons.

12 – 6 = 6 neutrons12 – 6 = 6 neutrons

How many neutrons in this How many neutrons in this atom?atom?

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NotationNotation

You might also see atomic mass You might also see atomic mass designated as C-designated as C-12 or O-1712 or O-17. The . The number following the symbol is the number following the symbol is the mass number - mass number - not the atomic not the atomic number.number.

With this designation you would With this designation you would have to look up the have to look up the atomic numberatomic number since it’s not designated.since it’s not designated.

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C-14C-14

1515NN77

Mass number = ?Mass number = ?Atomic number = ?Atomic number = ?# of neutrons = ?# of neutrons = ?# of electrons = ?# of electrons = ?

Mass number = ?Mass number = ?Atomic number = ?Atomic number = ?# of neutrons = ?# of neutrons = ?# of electrons = ?# of electrons = ?

Try these …

How many electrons in U-238?How many electrons in U-238? 9292How many neutrons in U-238?How many neutrons in U-238? 146146

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IonsIons Atoms can gain or lose ElectronsAtoms can gain or lose Electrons

This ability to gain or lose electrons This ability to gain or lose electrons determines how an element will react to determines how an element will react to form form bondsbonds

After an element that gains or loses one After an element that gains or loses one OR MORE electrons it is called an OR MORE electrons it is called an IONION

- - -

+-

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Positive IonsPositive Ions Gaining or losing electrons Gaining or losing electrons does not does not

affect the number of protons an affect the number of protons an element haselement has

When an atom loses an electron it When an atom loses an electron it becomes becomes POSITIVE (+)POSITIVE (+)

A Positive Ion is called an A Positive Ion is called an CationCation

Remember this as “Remember this as “C+C+ “ “

Note: The number of Note: The number of ProtonsProtons now now exceeds the number of exceeds the number of ElectronsElectrons

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Positive IonsPositive Ions Charge is indicated in the Charge is indicated in the Upper Upper

RightRight of the element symbol of the element symbol

Include the Sign of the charge plus Include the Sign of the charge plus the magnitudethe magnitude

Ex. +2, +3 Ex. +2, +3 Exception: +1 is written only as a + Exception: +1 is written only as a +

with no numberwith no number

Example:Example: Na Na Na Na++ + 1e + 1e- - (or Na - 1e(or Na - 1e--

NaNa+ + )) Cu Cu Cu Cu+2+2 + 2e + 2e--

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Negative IonsNegative Ions When an atom When an atom GAINSGAINS an electron it becomes an electron it becomes NEGATIVENEGATIVE

This Ion is called a This Ion is called a AnionAnion Remember this as “ A- “Remember this as “ A- “

The number of ELECTRONS now exceeds the number of The number of ELECTRONS now exceeds the number of protonsprotons

As before charge is written in the upper rightAs before charge is written in the upper right

Charge is now negative so the number is written with a Charge is now negative so the number is written with a “-” sign“-” sign

Cl + 1eCl + 1e-- Cl Cl-- S + 2eS + 2e-- S S-2-2

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IonsIons

N + 3 eN + 3 e-- N N-3-3

QUESTION (2): Nitrogen can gain QUESTION (2): Nitrogen can gain three electrons. Write the chemical three electrons. Write the chemical equation for the gain of these three equation for the gain of these three electrons. electrons.

QUESTION (1): Write the chemical QUESTION (1): Write the chemical equationequation

for the loss of 1 electron from the for the loss of 1 electron from the Rubidium atom?Rubidium atom?Rb Rb Rb Rb++ + 1 e- + 1 e-

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Putting it all togetherPutting it all together

How many protons, How many protons, neutrons, & electrons in neutrons, & electrons in each of the followingeach of the following::

2323NaNa+1+111113434SS-2-2

1616

1919FF-1-1

99

11 p, 12 n, 11 p, 12 n, 10 e10 e 16 p, 18 n, 16 p, 18 n, 18 e18 e 9 p, 10 n, 9 p, 10 n, 10 e10 e