Chemistry I – Unit 2 Notes Te x tbook Correlation Unit 2 consists of the following sections in the text: 4.1-4.3, 4.5-4.7, 4.10, 8.1, 11.1-11.9. 4.1 - The Elements A . An element is: B . Elements can exist as pure substances or as parts of compounds. Examples:
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Unit 2 consists of the following sections in the text:
4.1-4.3, 4.5-4.7, 4.10, 8.1, 11.1-11.9
John Dalton (1766-1844) – English Scientist page 78
Dalton’s Atomic Theory
1. Elements are made of tiny particles called atoms.
2. All atoms of a given element are identical (we now know that this is not exactly true)
3. The atoms of a given element are different from those of any other elements.
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 the atoms are grouped together.
A. J. J. Thomson’s Plum Pudding Model (1890’s) described atoms as being:
B. Ernest Rutherford’s “Nuclear” Model (1911) of the atom described the structure of atoms as follows:
1. Gold Foil Experiment (Rutherford) atom described the structure of atoms as follows:
A. From Rutherford’s gold foil experiment we learned that.
1. Atoms have a central positive nuclear charge
2. Atoms are 99.99% empty space.
B. Subatomic Particles
Also, for a neutrally charged atom,
Atomic Number = Number of Protons = Number of Electrons
*the atomic number determines the identity of an element
E. A “Box” in the Periodic Table: Structure
Use the equations above and your periodic table to fill in the missing values in the table below:
8.1 Weighted Average Atomic Mass the missing values in the table below:
A. What is a weighted average? Why do we need one?
An element can exist in a number of forms, called isotopes. Isotopes are forms of the same atom that vary in mass.
For example, there are two different types (isotopes) of copper atoms. One type of copper atoms weighs in at 62.93 amu, the other has a mass of 64.94 amu. The lighter isotope is more common with 69.09% of the naturally occurring copper having a mass of 62.93 amu per atom. The remainder of the atoms, 30.91 %, have a mass of 64.94 amu.
To find the Average Atomic Mass of an atom, we take into account all of the isotopes that exist and the percentage of each type. The calculation of the average atomic mass is weighted average.
B. How to calculate a weighted average atomic mass the missing values in the table below:
Take the sum of the products of each isotope’s mass and its corresponding relative abundance as a decimal (take percent and move decimal 2 places left).
Example 2 the missing values in the table below:
11.1 Rutherford’s Atom the missing values in the table below:
A. His model leaves many questions about electrons unanswered
1. How are the electrons arranged?
2. How do they move?
3. Since the nucleus and the electrons are oppositely charged, why doesn’t the atom collapse?
A. Parts of a wave
1. Wavelength is –
2. Frequency is –
A. Electrons can only absorb quantized amounts of energy…this means
B. With only one electron, a hydrogen atom is the simplest way to view what can happen when electrons get excited.
C. How can Hydrogen produce photons with 4 different energies (colors) when it only has 1 electron to excite? (See Figure 11.13 on pg. 310)
A. Bohr’s model of the atom included the following main points.
1. Central nucleus made up of ______________ and _______________.
2. Electrons were restricted to circular orbits.
A. Within each principal energy level there can be one or more orbitals.
1. “s” orbitals:
2. “p” orbitals:
3. “d” orbitals:
B. Each principle energy level is a little larger and further away from the nucleus than the last and contains more orbitals than the last.
A. Principle energy levels contain sublevels, which in turn contain orbitals.
B. Pauli exclusion principle: