Atoms, Ions, and the Periodic Table - Orange Coast Collegeocconline.occ.cccd.edu/online/avieau/Chp2NotesTWO.pdf · Atoms, Ions, and the Periodic Table ... electrons do not match the

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Copyright © McGraw-Hill Education. Permission required for reproduction or display. 2-1

Atoms, Ions, and the

Periodic Table

Copyright © McGraw-Hill Education. Permission required for reproduction or display.

2.1 Dalton’s Atomic Theory

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The scanning tunneling microscope, STM, invented in 1981, allows us to create images of matter at the atomic level.

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2.1 Dalton’s Atomic Theory: Mass is not gained or lost

in a chemical reaction.• Proposed by Antoine Lavoisier in 1787.• What would happen to the mass reading if the reaction was

done without the balloon (an open system)?

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Sodium carbonate +hydrochloric acid

Carbon dioxide + Sodium chloride

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2.1 Dalton’s Atomic Theory: A compound always has the

same relative amounts of the elements that compose it. • Proposed by Joseph Proust ~1800• For example, when water is broken down by electrolysis into

oxygen and hydrogen, the mass ratio is always 8 to 1.

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In 1808 John Dalton published a paper on atomic theory, summarized by the following postulates:• All matter is composed of small, indivisible particles, called atoms.• All atoms of a given element are identical both in physical and

chemical properties. Atoms of different elements have different physical and chemical properties.

• Atoms are not created or destroyed in chemical reactions.• Atoms combine in simple, fixed, whole-number ratios to form

compounds.

• In a chemical reaction, atoms rearrange into new combinations, obeying the Law of Conservation of Mass.

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Is the law of conservation of mass obeyed here?Is this process possible?

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:• Atoms actually are divisible. They are composed of subatomic

particles.• Subatomic particles found in the (dense center of the

atom)- positively charged subatomic particles

- uncharged subatomic particles• One kind of subatomic particle found outside the nucleus

- negatively charged subatomic particles

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• Protons, p+, are located in a tiny core at the center of the atom, the nucleus.

- charge = +1.6022 × 10−19 C (expressed as +1)- mass = 1.6726 ×10−24 g

• Neutrons, n, are also located in the nucleus- no charge - mass = 1.6749 ×10−24 g (~same mass as proton)

• The nucleus of the atom contains the p+ & n, and most of the mass of the atom.

• The diameter of an atom is about 10−10 meter. The diameter of the nucleus is about 10−14 m, 10,000 times smaller!

• The electrons, e-, occupy the empty space around the nucleus.- charge = −1.6022 × 10− 19 C (expressed as -1)- mass = 9.1094 ×10−28 g (insignificant to 4 SF’s)

• Although small in size, the nucleus accounts for about 99.9% of the mass of an atom.


2.2 Structure of an Atom

• Atoms of different elements differ by the number of protons in their nucleus.

• All atoms of an element have the same number of protons.

: the number of protons in an atom.• The atomic number is indicated in most periodic tables

above the element symbol.

: How many protons does a gold atom have?



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2.2 Structure of an Atom: the number of protons in the nucleus of an

atom: the number of protons and neutrons in the

nucleus of an element’s atom A = Z + Nthe number of neutrons in the nucleus of

an element’s atom N = A – Z

: an atom that contains a specific number of neutrons.• Many elements have multiple isotopes.• There are three isotopes of hydrogen:


: a notation that adds the mass number, A, and atomic number, Z, to the elemental symbol, X.

𝑋"#Representations for a carbon atom with 6 neutrons:

• 𝐶%&'

• carbon-12• C-12

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: Determine the number of protons and number of neutrons for this atom

• Write the isotopic symbol for this atom

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Write two representations for the following isotope.


: Write the isotopic symbol


Determine the number of protons and neutrons in each of the following isotopes:

• 𝐶𝑙&)*+

• 𝑐𝑎𝑟𝑏𝑜𝑛 −11

• 𝐴𝑢&67

Practice writing the isotope symbols for the following isotope pairs.

1. carbon-13 and carbon-142. chlorine-35 and chlorine-37

3. uranium-235 and uranium-238 4. lithium-6 and lithium-7

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: Write the isotopic symbol

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: Heavy waterOne ice cube is made with water that contains only the hydrogen-2 isotope.

The other ice cube is composed of water with normal water which contains mostly hydrogen-1.

• Which ice cube is made with H-2?

• How can you tell?

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2.3 Ions

Ions differ from atoms in that they have a charge; the number of electrons do not match the number of protons.

: positively charged ions. • They have fewer electrons than in the neutral atom.• Cations are named by adding ion to the elemental name

- Na+ is sodium ion

: negatively charged ions.

• They have more electrons than in the neutral atom.• Anions are named by adding –ide ion to the prefix of the

elemental name- Cl- is chloride ion


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2.3 Ions


2.3 Ions


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: Counting Protons & Electrons

Write the name, number of protons & number of electrons for the following ions:

1. Li+

2. F−

3. O2−

4. Al3+

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: Ion Names & SymbolsWrite the name and symbol for the ion that have the following:1. 20 protons and 18 electrons

2. 16 protons and 18 electrons

3. 26 protons and 23 electrons


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2.4 Atomic Mass


We can use mass number to compare the approximate relative masses of different isotopes.• A carbon-12 atom is about twelve times the mass of a hydrogen-

1 atom.• An oxygen-16 atom is about four times the mass of a helium-4

atom.• But keep in mind that the mass number is NOT an actual mass!

: A technique used to determine:• the individual masses of the isotopes • relative amounts of the isotopes in a sample

2.4 Atomic Mass: AMU Scale

: atomic mass units, 1/12 mass of 1 C-12 atom The mass of a carbon-12 atom is 1.99272×10−23 g. Because this is such a small number, the amu scale was developed and based on the mass of carbon-12:

• 1 amu = 1/12 mass of 1 C-12 atom = 1.6606×10−24 g

• Carbon-12 has a mass of exactly 12 amu per atom.


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2.4 Atomic Mass: Relative Atomic Mass• Most elements have more than one isotope. • If we average the masses of all the isotopes of carbon, taking

into account the relative amounts of each, we get a relative atomic mass of 12.011 amu.

- This value is pretty close to 12 since carbon-12 is the mostabundant isotope.

: the average mass of the individual isotopes of an element, taking into account the naturally-occurring relative abundance of each• This is the mass represented on Periodic Tables.

: The relative atomic mass of silver is 107.9 amu, as found on the Periodic Table

• If silver is composed of only Ag-107 and Ag-109, which isotope is most abundant?



2.4 Atomic Mass: Relative Atomic MassMass contribution from isotope (MC) = Isotope mass ×relative abundanceRelative Atomic Mass = MC1+ MC2 + …

: An unknown element (X) discovered on a planet in another galaxy was found to exist as two isotope, with masses and abundances as listed in the table.

What is the relative atomic mass of the element?

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Isotope Mass (amu) Natural Abundance 22X 21.995 75.00 %20X 19.996 25.00 %

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2.5 The Modern Periodic Table


K reacts violently with water to producing a basic solution and

flammable hydrogen gas. All alkali metals react with water to

produce hydrogen gas.

Our current periodic table shows elements in order of increasing atomic number (number of protons.)

or : Elements in the same column having similar properties. Groups are designated in 2 ways:

1. A Roman numeral (I through VIII) and a letter (A or B)2. An Arabic number (1-18)

: Horizontal row of elements having properties that tend to vary in a regular fashion. Periods are designated by Arabic numbers.


2.5 The Modern Periodic Table: GroupsSome groups have descriptive names that are commonly used instead of their group numbers.

: Group 1 (IA) metals (not hydrogen)• are considered reactive because they react readily with other

elements and compounds• React with water to produce hydrogen gas

: Group 2 (IIA) metals• are more reactive than the transition metals but less reactive than

alkali metals

: Group 17 (VIIA) nonmetals• exist naturally as diatomic molecules (2 atoms)

: Group 18 (VIIIA) nonmetals• also called inert gases• they do not chemically react with other elements under normal

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2.5 The Modern Periodic TableThe periodic table has many classifications:

Groups (columns) and periods (rows)• Groups have similar properties• Periods have properties that vary in a pattern

Metals, nonmetals, and metalloids.• Metals are lustrious, malleable, ductile, and conduct heat &

electricity• Nonmetals are dull, brittle and heat & electrical insulators.• Metalloids are elements that have physical properties

resembling a metal, but the chemical reactivity of a nonmetal.

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2.5 The Modern Periodic Table


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2.5 The Modern Periodic Table: contain any element in the eight

groups designated with the letter A. (In the Arabic numbering, groups 1, 2, and 13-18)

: contain any element in the 10 groups designated with the letter B. (In the Arabic numbering, groups 3-12)

: contain the lanthanides and actinides listed separately at the bottom of the table.

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2.5 The Modern Periodic Table: occur in

pairs when not combined with other atoms• Most elements do not exist as

single atoms. • Notable exceptions: Noble

gases

• 7 elements exist naturally as diatomic molecules in their elemental form.

• N2, O2, F2, Cl2, Br2, I2 & H2

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2.5 The Modern Periodic Table: Ions

• When alkali metals, such as sodium, reacts to form ions, the ions have a 1+ charge.

• The alkaline earth metals, such as magnesium, form ions with a 2+ charge.

• Oxygen and other chalcogens react to form ions which have a 2− charge.

• The fluorine and other halogens form ions with a 1−charge.

• The noble gases do not form ions.• How can we explain or predict this pattern?



2.5 The Modern Periodic Table: IonsThe noble gases are the most stable (least reactive) elements on the periodic table. • Their stability is associated with the number of electrons

they contain.

Many atoms in the main-group elements gain or lose electrons to obtain the same number of electrons as the nearest noble gas.• Metals tend to lose electrons

- become cations- to have the same number of e-’s as the last noble gas.

• Nonmetals tend to gain electrons, - become anions- to have the same number of e-’s as the next noble gas

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2.5 The Modern Periodic Table: Common Monatomic Ions


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Atoms, Ions, and the Periodic Table - Orange Coast Collegeocconline.occ.cccd.edu/online/avieau/Chp2NotesTWO.pdf · Atoms, Ions, and the Periodic Table ... electrons do not match the