Unit 3 Particles with Internal Structure. The Elements Remember, elements are combined to form molecules the way letters are combined to form words.

Unit 3 Particles with

Internal Structure

The Elements Remember, elements are combined to form

molecules the way letters are combined to form words.

Presently there are about 115 known elements.

Only 88 occur naturally, the rest are made in laboratories.

Only 9 elements account for most of the compounds found in the Earth’s crust.

Table 3.1

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All living things are made up, mainly, of oxygen, carbon, hydrogen and nitrogen.

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Symbols For The ElementsJust as each state has a two-letter

abbreviation, each element has a one- or two-letter symbol to make life simple for chemists.

Some elements found in the human body are: As, Cr, Co, Cu, F, I, Mn, Mo, Ni, Se, Si, & V.

Notice the first letter is ALWAYS capitalized and the second letter, if present, is Not capitalized.

Symbols For The ElementsSome symbols make sense like O

for oxygen and H for hydrogen or Ni for nickel.

Others, like Pb for lead or Fe for iron, don’t automatically make sense; they originated from the Greek or Latin names of plumbum (Pb) and ferrum (Fe).

Dalton’s Atomic TheoryScientists studying matter in the

eighteenth century made the following observations:Most natural materials are mixtures of pure substances.

Pure substances are either elements or combinations of elements called compounds.

A given compound always contains the same proportions (by mass) of the elements.

John Dalton attempted to explain these observations in 1808.

Dalton’s Atomic Theory1. Elements are made of tiny particles called

atoms.2. All atoms of a given element are

identical.3. The atoms of a given element are

different from those of any other element.

4. Atoms of one element can combine with atoms of other elements to form compounds. A given compound always has the same relative numbers and types of atoms.

5. Atoms are indivisible in chemical processes. That is, atoms are not created or destroyed in chemical reactions. A chemical reaction simply changes the way atoms are grouped together.

Formulas of Compounds

The types of atoms and the number of each type in each unit (molecule) of a given compound are conveniently expressed by a chemical formula.

The atoms are indicated by their symbols and the number of each type is indicated by a subscript (unless there is only one).Ex) C6H12O6 or H3PO4

Practice Write the formula for each of the

following compounds, listing the elements in the order given:

a. A molecule contains four phosphorous atoms and ten oxygen atoms.

b. A molecule contains one uranium atom and six fluorine atoms.

c. A molecule contains one aluminum atom and three chlorine atoms.

What is inside an atom?

Build an Atom Activity

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Modern Atomic StructureEvery atom is composed of the three

basic subatomic particles. (Protons, electrons, neutrons)

Different elements have different numbers of each of these subatomic particles.

The reason one element behaves differently than another lies in the number and arrangement of their electrons.

When atoms get close to each other their electron “clouds” can overlap and interact.

Figure 3.9: A nuclear atom viewed in cross section.

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In any box on the Periodic Table, what information can you find?

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Atomic number = number of protons, unique for every element, no 2 elements have the same atomic #

Element symbol = can be 1,2 or 3 letters, first letter is always capitalized, and succeeding letters are always lower case

Average Atomic Mass = Protons + Neutrons

the weighted average of all the mass numbers for each isotope of the element

IsotopesTwo atoms of the same element (same

number of protons) with different numbers of neutrons.

Figure 3.10: Two isotopes of sodium.

Isotopes There are two important numbers

associated with any given element:1. Atomic Number – The number of

protons in a nucleus. 2. Mass Number – The SUM of the

number of protons AND neutrons (a.k.a. nucleons) in a nucleus (NOT the sum of their masses).

We should note that two different isotopes will have the same atomic number, but different mass numbers.

IsotopesThe two previous examples of isotopes of sodium would be:

1123Na 11

24Na• The example on the left would contain 11 protons and 12 neutrons (23-11=12).

• The example on the right would contain 11 protons and 13 neutrons (24-11=13).

Practice Problems Write the symbol for each of the

following atoms, and list the number of protons, neutrons, and electrons for each.

1) The cesium atom with a mass number of 132.

2) The iron atom with a mass number of 56.

3) The krypton atom that has 48 neutrons.

4) The nitrogen atom that has 6 neutrons.

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M&M Isotope Lab

Weighted Average Atomic Mass Remember elements can have different isotopes

which means that they vary in their number of neutrons.

If you have 3 different isotopes of the same element: 15 atoms have a mass of 21 8 atoms have a mass of 23 2 atoms have a mass of 19We can calculate the weighted average by

multiplying the number of atoms by their mass:

(15) (21) = 315 537 = 21.48 (8) (23) = 184 25 (2) (19) =+ 38 average atomic

mass 537

Using % to find Average Atomic Mass Usually we only know the percents of

various isotopes that make up different elements, we can use this to calculate the average atomic mass.

If we have 100% chlorine:75.77% of mass is 35 .7577x35 = 26.5224.23% of mass is 37.2423x37= 8.96

Add the 2 together to get the atomic mass:

26.52+ 8.96 = 35.48

Practice Oxygen has 3 isotopes 16O, 17O, 18O 99.76% of mass is 16O

0.04% of mass is 17O0.20% of mass is 18O

What is the average atomic mass?

Find the atomic mass if 99.64% of mass is 14N and 0.36% is 15N.

A Simple Version of the Periodic Table

Periodic TableWhen looking at periodic table elements are

arranged in horizontal rows by increasing atomic number.

Horizontal rows are called “Periods”. Periods go left to right

Periodic TableThe vertical columns are called “Groups” or

“Families”Elements in families share similar properties

Metals, Semimetals, Non-MetalsAll elements on the periodic table are grouped as metals, semimetals or metalloids, or non-metals. Due to the arrangement of the periodic table, it is easy to identify each type of element.

Figure 3.12: Elements classified as metals and nonmetals

Metals: Fall to left and under the stairs Properties of Metals:

Efficient conduction of heat and electricity

Malleability

Ductility

A lustrous appearance

Positively charged ions

Non-Metals: Right and above the stairs• Dull, Brittle• Negatively charged ions• Nonconductors

-insulators

Semimetals or Metalloids: Makeup the stairs• Properties of both metals and non-

metals• Semiconductors

Lanthanide and Actinide Series

Mostly human made elements Radioactive elements

Group 1A – Alkali Metals

Group 2A – Alkaline Earth Metals

Group 7A or 17: Halogen Family

Group 8A or 18: Noble Gases

Do not react easily with anything, due stable electron configuration

All other elements strive to reach noble gas configuration for maximum stability by reacting with other elements.

Transition Metals: Group 3B-12B

Who is a solid, liquid or gas?

When we look at the elements on the periodic table, who is a solid, liquid or gas in their natural state?

Most elements are not found in their elemental state, most elements are found in compounds with other elements.

Most elements on the periodic table are solids, so we will point out those who are gas or liquid.

LiquidsOnly 2 elements in their elemental form are a liquid at 25 degrees Celsius: Mercury and Bromine

GasesMore elements exist in

their elemental form as a gas, but there are some important distinctions to make about these gases.

The noble gases are a gas, called monatomic gases. The prefix mono- means one. And monatomic gases exist as individual atoms.

Figure 3.13: A collection of argon atoms.

Gases

There is another group of gases called diatomic gases. The prefix di- means two. These elements travel in pairs as molecules.

Figure 3.14: Oxygen gas contains OXO molecules.

Figure 3.14: Nitrogen gas contains NXN molecules.

Diatomic moleculesThere are 7 elements that exist as diatomic molecules, you will simply need to find a way to memorize these.

If you notice, all of the halogens fall in this category, and then hydrogen, nitrogen, and oxygen.

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What is an ion?When we discussed atoms before, we were

always looking at a neutral atom.Neutral atoms always have equal numbers of protons and electrons.protons = +1 charge electrons = -1 charge

When atoms have unequal numbers of protons and electrons, then the atom is a charged particle called an ion.

Ion FactsIons are atoms, or groups of atoms,

with a charge.The charge is created by different

numbers of protons and electrons.In an atom ONLY electrons can

move.Atoms gain or lose electrons to

become ions.

Cations and AnionsThere are 2 types of ions: cations and anions.Cations are ions with a (+) positive charge. To form

a cation, an atom has lost electrons.Example: Na loses an electron and becomes Na+

Anions are ions with a negative charge. To form an anion, an atom has gained electrons.Example: Cl gains an electron and becomes Cl-

Basic Names for IonsCations do not change names from their

neutral atoms. Example: Magnesium loses 2 electrons and becomes Mg2+ which is named magnesium ion.

Anions change the end of their name to –ide.Example: Chlorine gains an electron and becomes Cl-. We would change the name from chlorine to chloride.

Some Common Anion NamesWhat would the names of the following

ions be?Chlorine = Fluorine =Bromine =Iodine =Oxygen =Sulfur =

How to Determine the ChargeWhen determining the charge for an atom

we can use the periodic table to help.The number of valence electrons

determines the charge.All atoms want 8 valence electrons. If an atom has 1-3 valence electrons the

atom will lose them to become positive.If an atom has 6-8 valence electrons the

atom will gain electrons to become negative.

We can determine the charge by looking at the periodic table.

Figure 3.19: The ions formed by selected members of groups 1, 2, 3, 6, and 7.

PracticeDetermine the name and charge of the

following ions:PotassiumBromineCalciumSulfurAluminumStrontiumCesium