UNIT: Matter

Objectives: Lesson 4 of 4• You will review the structure of the atom• You will learn the difference between the Atomic Number and Mass

Number for an element• You will learn what an isotope is• You will learn what an ion is and how they form• You will learn the difference between a cation and anion

TOPIC: Atoms, Isotopes and Ions

QuickwriteIn 1-2 sentences answer one of the questions below:• Review: What components do you think make up an

atom???

• What is in the nucleus of an atom?

• How big is the nucleus of an atom when compared to the entire atom?

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Atoms• All matter is made of tiny particles

called Atoms• An atom is the smallest particle of an

element that has the properties of that element

• Atoms are composed of a dense center region called a nucleus

• The nucleus is made up of positive particles called protons and neutral particles called neutrons

• Atoms are also made up of an outer electron “cloud” where negatively charged particles known as electrons can be found

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-Nucleus

Protons

Electrons

Neutrons

• Imagine an atom is the size of a baseball stadium

• On this scale, the nucleus would be about the size of a pea on the pitcher’s mound

• The electron “cloud” and electrons that surround the nucleus would occupy the size of the stadium

• The electron cloud is essentially an unoccupied region of space, so an atom is really just empty space

Actual Size of the Nucleus

What is an Atom?• Smallest particle of an element

that has the properties of that element

• It is made up of:– An incredibly small, dense center

called a nucleus– The nucleus is made up of positively

charged particles called protons and neutral particles called neutrons

– A region of empty space known as the electron “cloud” where negatively charged particles called electrons can be found

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-Nucleus

Protons

Electrons

Neutrons

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Atomic Mass Unit (AMU)• What if we could weigh or mass a proton on a scale?• How much do you think it would it weigh?• The actual mass of a proton is 1.66 x 10-24 grams

1.6 x 10-24 gms

+• It turns out that a neutron has about the same

mass: 1.66 x 10-24 grams• That’s an incredibly small number to work with• A more convenient unit to measure the mass

of a proton or neutron is the Atomic Mass Unit or AMU

• 1 AMU = 1.66 x 10-24 grams and is defined as 1/12 the mass of a carbon-12 atom

1.6 x 10-24 gms

• A carbon-12 atom has 6 protons & 6 neutrons, so 1 AMU is basically the mass of 1 proton or neutron

• Electrons are so light that you can usually ignore their mass relative to the atom as a whole

• Remember, all the mass or weight in an atom is in the nucleus

• A proton has about 2000 times the mass of an electron

What is an Atomic Mass Unit (AMU)?

• 1 AMU = 1.66 x 10-24 grams and is defined as 1/12 the mass of carbon-12 atom

• 1 AMU is the mass or weight of a proton or neutron

Atomic Number and Mass Number• Atomic number is the number of protons each element has• For example, Carbon here has six protons• The numbers of protons determines the identity of the element• The periodic table is listed in order of increasing atomic number• For example, Hydrogen, the lightest element has 1

proton• Helium, the next heaviest element has 2 protons• Lithium has 3 protons……

Atomic Symbol, Atomic Number and Mass Number• Recall that every element on the periodic table is represented by an

atomic symbol• The atomic symbol is a one or two letter symbol used to represent

every element on the periodic table• The atomic symbol for Carbon is represented by a capital C• Every Element can also be represented by a mass number and

atomic number • The atomic number is the number of protons in the element• Remember, it is the amount of protons that determine the element• Carbon always has 6 protons, so the atomic number is 6 or 6 AMU• The mass number is equal to the number of protons plus neutrons• For carbon, it is 6 protons plus 6 neutrons, which is equal to 12 or

12 AMU

6C12

Atomic Symbol

Mass Number

Atomic Number

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Atomic Symbol, Atomic Number and Mass Number

2He 4

Atomic Symbol

Mass Number

Atomic Number

• Here is a Helium Atom• The atomic symbol for

Helium is represented by He• Notice, the nucleus contains

two protons, therefore it’s atomic number is 2 or 2 AMU

• You may have also noticed that Helium nucleus has 2 two neutrons

• Remember, the mass number is equal to the number of protons plus neutrons therefore it’s mass number is equal to 4 or 4 AMU

Symbol Name Number of Protons

Atomic Number

Number of Neutrons

Mass Number

Helium-4 22 2 4

What is the difference between the Atomic Symbol, Atomic Number and Mass Number?

• The atomic symbol is a one or two letter symbol used to represent every element on the periodic table

• The mass number is equal to the number of protons plus neutrons• The atomic number is the number of protons in the element• Please draw:

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Isotopes

2He 4

Atomic Symbol

Mass Number

Atomic Number

• Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons

Symbol Name Number of Protons

Atomic Number Number of Neutrons

Mass Number

Helium-4 22 2 4

• What would happen if we added another neutron to the nucleus?

• How does the mass number change if added another neutron?

• Let’s find out and add another neutron• Notice, the number of protons and the

atomic number did not change,• However, because we added a

neutron the mass number increased from 4 to 5

• Remember, the number of protons determines the atom or element

• Lets take a look at our helium atom again

• Recall that helium has two neutrons and two protons in its nucleus giving it an atomic number of 2 and a mass number of 4

Helium-5 22 3 5

• What would happen if we added another neutron to the nucleus?

• How does the mass number change if added another neutron?

• Let’s find out and add another neutron• Notice, the number of protons and the

atomic number did not change,• Once again, because we added a

neutron the mass number increased from 5 to 6

5 6

Helium-6 22 4 6

Isotopes

6C12

Atomic Symbol

Mass Number

Atomic Number

• Here we have a Carbon-12 atom with six protons and six neutrons

• Carbon-12 is not an isotope because we have an equal amount of protons and neutrons

• One of the most common isotopes scientists work with is the Carbon-14 isotope

• To make a Carbon-14 isotope, we need to add two neutrons to Carbon-12 seen here

• So, let’s add two neutrons to Carbon-12• Notice, the number of protons and atomic

number did not change, but, because we gained two neutrons, the mass number went from 12 to 14

Symbol Name Number of Protons

Atomic Number

Number of Neutrons

Mass Number

Isotope Yes or No?

Carbon-12 66 6 12 NO

14

6 6 8 14 YESCarbon-14

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What is an Isotope?• Atoms of the same element that have the same number of protons

but different numbers of neutrons• Example: Carbon-14 ( ) and Helium-6 ( )

Ions• A ion is an atom(s) that has lost or

gained one or more electrons giving it an overall charge

• For example, here we have a neutral Sodium atom

• A neutral sodium atom has 11 protons and 11 electrons going around the nucleus

• What makes it neutral?• Remember, protons have a +1 charge

and electrons have -1 charge • The fact that it has an equal amount of

protons and electrons gives it a charge of zero

• Or we can do the math and see that -11 + 11 = 0

• But sodium is an atom that is known for losing an electron

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11 protons (+11 Charge)

11 electrons (-11 Charge)

Sodium Atom Neutral (+0 charge)

Ions• If an ion is an atom(s) that has

lost or gained one or more electrons giving it an overall charge, What do you think would happen if sodium here lost an electron?

• What kind of charge will the sodium have on it after it loses an electron?

• Let’s find out and remove the outer electron

• Notice, there are still 11 protons in the nucleus, but now there are 10 electrons

• Because it has an additional proton, the sodium atom now has a +1 charge, forming a +1 Ion

• Once we could do the math to verify this: -10 + 11 = +1

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11 protons (+11 Charge)10 electrons

(-10 Charge)

Sodium Atom

+1

What is an Ion?• An atom(s) that has lost or gained one or more electrons giving it

an overall charge• Example: sodium ion (Na+1)

Cations versus Anions• A cation is a positive ion because it

has lost one or more electrons• For example, here we have a

neutral Magnesium atom • A neutral Magnesium atom has 12

protons and 12 electrons going around the nucleus

• What kind of Ion will form if Magnesium here lost 2 electrons?

• Let’s find out and remove the outer 2 electrons

• Because it has two additional protons, the Magnesium atom now has a +2 charge, forming a +2 Cation

• Once again we could do the math to verify this: -10 + 12 = +2

• Metals (such as Magnesium) typically lose electrons to become cations

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12 protons (+12 Charge)

12 electrons (-12 Charge) +210 electrons (-10 Charge)

Magnesium Atom

Cations versus Anions• A anion is a negative ion because it

has gained one or more electrons• For example, here we have a neutral

Fluorine atom • A neutral Fluorine atom has 9

protons and 9 electrons going around the nucleus

• What kind of Ion will form if Fluorine here gained 1 electron?

• Let’s find out and ADD 1 electron• Because it has one additional

electron, the Fluorine atom now has a -1 charge, forming a -1 anion

• Once we could do the math to verify this: -10 + 9 = -1

• Nonmetals (such as Fluorine) typically gain electrons to become anions

• When an atom becomes an anion, we change the ending and add -ide

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9 protons (+9 Charge)

9 electrons (+9 Charge)

Fluorine Atom -110 electrons

(-10 Charge)

What is the difference between a Cation and an Anion?

• A cation is a positive ion formed when an atom loses one or more electrons

• Metals typically lose electrons to become cations• Example: Sodium (Na1+) & Magnesium (Mg2+) cation

• A anion is a negative ion formed when an atom gains one or more electrons

• Nonmetals typically gain electrons to become anions• Example: Fluoride (F1-) & Sulfide (S2-) anion

Symbol Name Number of Protons

Atomic Number

Number of Neutrons

Mass Number

Isotope Yes or No?

Number of Electrons

Charge

Carbon-12 66 6 12 06NO

Practice:• Complete the table below

Answer: -Because there are 6 protons, the atomic number must be 6 as well.-The mass number is equal to the amount of protons + neutrons, so the mass number must be 12-Because the amount of the protons is the same as the amount of neutrons, the atom is NOT an isotope-Because the charge is zero, their must be an equal amount of protons and electrons, so in this case, because there are 6 protons, so, their must be 6 electrons-Since we know the mass number and atomic number, we can write the symbol

Symbol Name Number of Protons

Atomic Number

Number of Neutrons

Mass Number

Isotope Yes or No?

Number of Electrons

Charge

Hydrogen-3 11 2 3 +10YES

Practice:• Complete the table below

Answer: -Because the atomic number is 1, the amount of protons must be 1 as well -The mass number is equal to the amount of protons + neutrons, so, 1 + 2 = 3, therefore the mass number is 3-Because there are more neutrons than protons, the atom IS an isotope-Because we have no electrons and 1 proton, this give the atom a +1 charge -Since we know the mass number and atomic number, we can write the symbol (this particular isotope of hydrogen is called tritium and is highly radioactive)

Summarize:(you can always write you own)

• What is an atom made up of? Where is the mass of an atom located? What part of the atom is made up of “empty space”

• Explain why it is more convenient to work with AMU’s (Atomic Mass Unit’s) versus grams: (In other words, which number would you rather work with, 1 AMU or 1.66 x 10-24 grams?)

• Compare and contrast the atomic number with the mass number, what's the difference?

• What are isotopes? How do isotopes affect the mass number of an atom?

• How do atoms become cations and anions?