unit 3 particles with internal structure. the elements remember, elements are combined to form...
TRANSCRIPT
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