Unit 1 notes 2Intro to parts of the atomIntro to parts of the atom

Synopsis of Structure• The atom is the smallest part of an element The atom is the smallest part of an element

that retains its properties.that retains its properties.• It is made of mostly empty space,with the It is made of mostly empty space,with the

majority of the mass concentrated in the majority of the mass concentrated in the middle (the nucleus).middle (the nucleus).

• The nucleus contains the positively charged The nucleus contains the positively charged protons and the chargeless neutrons.protons and the chargeless neutrons.

• The electrons are situated outside of the The electrons are situated outside of the nucleus in the empty space innucleus in the empty space inenergy levels (more on this lenergy levels (more on this later).r).

Warning: Oversimplification Ahead

Atomic number, mass number,atomic mass & isotopes

Atomic Number• The atomic number of an element tells The atomic number of an element tells

you the number of protons in the you the number of protons in the nucleus.nucleus.

• Atoms are electrically neutral Atoms are electrically neutral when when found in elemental formfound in elemental form, so the , so the number of protons will be the same as number of protons will be the same as the number of electrons.the number of electrons.

• Each element has a different atomic Each element has a different atomic number. number.Atomic

number

Answer the following

•What element has atomic What element has atomic number 32?number 32?

•How many protons does helium How many protons does helium have?have?

•What element has 79 protons?What element has 79 protons?•What is uranium’s atomic What is uranium’s atomic

number?number?•How many electrons does a How many electrons does a

neutral atom of calcium have?neutral atom of calcium have?

Mass number• Most of the mass of an atom is in the Most of the mass of an atom is in the

nucleus; so much that the electrons nucleus; so much that the electrons can be neglected.can be neglected.

• The mass number is the number of The mass number is the number of protons and neutrons in the nucleus.protons and neutrons in the nucleus.

• If you know the mass number and the If you know the mass number and the atomic number, you can determine atomic number, you can determine the composition of an atom.the composition of an atom. # of neutrons = mass number – # of neutrons = mass number –

atomic numberatomic number

Mass number, cont’d.• Composition can be written in Composition can be written in

shorthand by putting the symbol for shorthand by putting the symbol for the element with the mass number and the element with the mass number and atomic number to the left.atomic number to the left.

C126

• Or, the mass number and Or, the mass number and chemical element can designate chemical element can designate atoms, such as in:atoms, such as in:

Carbon-12

•How many neutrons are in How many neutrons are in potassium-39?potassium-39?

•How many protons are in lead-How many protons are in lead-208?208?

• If an element has 22 protons and If an element has 22 protons and 26 neutrons, what is its mass 26 neutrons, what is its mass number?number?

•What element is in the previous What element is in the previous question?question?

•How many neutrons are in ?How many neutrons are in ?

Answer the following

HgHg202011 8080

Isotopes• Atoms of the same element Atoms of the same element

always have the same number of always have the same number of protons, but can have different protons, but can have different numbers of neutrons.numbers of neutrons.

• An atom with the same number of An atom with the same number of protons but different number of protons but different number of neutrons are called neutrons are called isotopesisotopes..

• Isotopes are chemically alike, Isotopes are chemically alike, because it is the protons which because it is the protons which are responsible for the chemical are responsible for the chemical behavior.behavior.

•What is the difference What is the difference between iodine-127 and between iodine-127 and iodine-125?iodine-125?

• Is an element with 25 protons Is an element with 25 protons and 30 neutrons an isotope and 30 neutrons an isotope of one with 26 protons and of one with 26 protons and 30 neutrons? Why or why 30 neutrons? Why or why not?not?

Answer the following

Elements in CompoundsElements in Compounds

•When atoms chemically combine to make compounds, many times they lose or gain electrons.

•Unequal numbers of protons and electrons means that the particle is charged.

• Instead of calling these atoms, we call these ionsions.

Elements in CompoundsElements in Compounds

•Metals tend to lose electrons in compounds, making them positive.

•Nonmetals tend to gain electrons in compounds, making them negative

MetalsMetals

Non-Non-metalsmetals

•How many electrons are in How many electrons are in CaCa2+2+??

•How many electrons are in How many electrons are in OO2-2-??

•How many protons are in How many protons are in PP3-3-??

Answer the following

Atomic mass• Because there can be several

isotopes of an element, there is another number, the atomic mass, that is the weighted average mass of all an element’s isotopes.

• Carbon-12 was used as a reference to measure mass of atoms, and the carbon-12 atom was said to have a mass of exactly 12 amu’s.

Atomic mass

Finding Weighted Avg.• Take into account both the mass of

all isotopes as well as their relative abundances. For example:

• There are two known stable isotopes of carbon; carbon-12 and carbon-13. If 99.0% is carbon-12 and the rest is carbon-13, what is the average atomic mass of carbon?

Finding Weighted Avg.• Zinc has five naturally occurring

isotopes; zinc-64 (48.89%), zinc-66 (27.81%), zinc-68 (18.57%), zinc-67 (4.11%) and zinc-70 (0.62%). Based on this, what is the average atomic mass of zinc?

Elements and the Periodic Table

Arrangement of the table

• The periodic table is arranged in order of increasing atomic number.

• They are in groups according to similar chemical and physical properties.

• What gives them similar properties?

Arrangement of the table

• Elements in the same group have the same number of valence electrons.

• This means they tend to lose or gain electrons in bonding the same way and make similar compounds.