Slide1 : Basic Chemistry (Review)
Slide2 : Atoms and Elements It is important to understand the fundamental difference between atoms and elements when looking at biological compounds. Your book offers these definitions:
Element – a fundamental form of matter with the same chemical and physical properties that can’t be broken down into any more unique parts by ordinary chemical or physical means
Atom – the smallest particles of matter that retain all of the properties of an element
The best way to think about the difference is with an example. Let’s say that I had a brick of pure gold. This would be an element, because no matter how many times I broke it’s many atoms apart, every atom would still be gold.
Slide3 : Components of the Atom Every atom of every element consists of three basic components, the proton, the neutron, and the electron
Slide4 : Parts of the Atom An atom consists of two very different parts, the nucleus and the electron cloud.
Atomic Nucleus – is an extraordinarily small, extremely dense region in the center of an atom which contains all of the atom’s protons and neutrons
-- the nucleus contains over 99.9% of the mass of an atom
-- the size of the nucleus compared to the size of the atom is like a marble in a football field
-- discovered by Rutherford’s gold-foil experiment
Electron Cloud -- rest of the atom which surrounds the nucleus, which contain free-moving electrons
Slide5 : What Makes an Atom an Element? Every element is unique because it requires a specific kind of atom.
What element an atom is depends solely on the number of protons in that atom’s nucleus.
We refer to the number of protons in an atom’s nucleus as the atom’s atomic number
You can find the atomic number of any atom on your periodic table by looking in the upper left-hand corner of the box for that element
Remember: Atomic Number = # of protons
Slide6 : Atomic Mass If we know that the mass of a proton is 1 amu, the mass of a neutron is 1 amu, and the mass of an electron is 0 amu, then the mass of an atom (in amu) is simply the mass of the protons plus the mass of the electrons.
Even simpler, because the mass of protons and neutrons are each 1,
Atomic Mass = # of Protons + # of Neutrons
You can find the atomic mass of any element under the element’s name on the periodic table.
On my periodic table, the masses aren’t whole numbers, why is that?
Since atoms can only have whole protons and whole neutrons, it makes sense that the atomic mass of any element should be a whole number, however, the mass given on the periodic table isn’t a whole number. Instead, it’s an average mass of all of the isotopes of an element. Which brings us to. . .
Slide7 : Isotopes We know that every atom of an element has to have the same number of protons or it would be a different element. Every atom of a particular element, however, does NOT have to have the same number of neutrons, and therefore every atoms of the same element does not have to have the same atomic mass.
Isotopes – two atoms of the same element with different atomic masses
Some common isotopes:
carbon-12 and carbon-14 atomic mass
oxygen-16 and oxygen-18
hydrogen, deuterium, and tritium (H-1, H-2, H-3)
Slide8 : Charge! Usually, atoms of an element are neutral in charge (think about what would happen if they weren’t!), however sometimes an atom picks up an electric charge.
For an atom to be neutral in charge, it must have the same number of positively-charge protons (+) as negatively-charged electrons (-). It is when this atom gains or loses an electron that it gains or loses a positive or negative charge.
*** Atoms cannot gain or lose protons or they will become new elements!!! impossible without fission/fusion
Slide9 : Ions When an atom gain or loses an electron to become positively or negatively charged, we call it an ion
Atom gains electron negatively charged
Atoms loses electron positively charged
Writing ions:
when we write an ion of an atom, we always put the charge in superscript to the right of the atomic symbol
Examples:
Sodium with one less electron = Na+
Chlorine with an extra electron = Cl-
Sulfur with two extra electrons = S2- or S-2
Slide10 : Using our periodic table and what we know about atomic number, mass, isotopes, and electrons, we can fill in the following chart:
Slide11 : Electrons Atoms which are not ions have the same number of protons as electrons.
These electrons are arranged in different energy levels, a topic which will be discussed later in chemistry and physics.
For now, we will use the simplest model of describing the location of electrons, which is known as the Bohr model.
-- Designed by scientist Neils Bohr to represent the energy level of an electron in a hydrogen atom
-- The Bohr model only can be correctly drawn for elements 1-18
-- The Bohr model is actually only a correct model for the hydrogen atom
Slide12 : Using the Bohr Model The Bohr Model assumes that each energy level can hold eight electrons, EXCEPT for the lowest (1st) energy level, which can only hold two electrons.
The electrons in the highest energy level are called valence electrons
Example of Bohr Model for Flourine (9 p+, 9 e-): 9 p+
10 n e- e- e- e- e-
e- e- e- e- Notice that fluorine has 2 electrons in its lowest (1st) energy level, and 7 electrons in its valence energy level
Slide13 : Using our periodic table, we can easily draw Bohr Models of elements and ions 1-18 on the periodic table:
Li (Lithium) N (Nitrogen) Cl- (Chlorine -1)
Slide14 : Valence Electrons Valence electrons play a very important role in bonding
Atoms like to have full valence shells of 8 electrons, therefore, atoms will share valence electrons with atoms of other elements to make compounds.
For example: Water (H2O) has two hydrogen atoms and one oxygen atom.
Oxygen = 6 valence electrons
Hydrogen = 1 valence electron
Hydrogen = 1 valence electron
TOTAL = 8 shared valence electrons
Slide15 : The Periodic Table In addition to being a really spiffy-looking chart that tells us atomic number, mass, and symbol, the periodic table tells us other secrets about atoms as well.
The secrets are held in the rows and columns of the periodic table, which are known as periods and groups, respectively
Slide16 : Columns (Groups) Columns – the columns of the periodic table are called groups
-- Each group is numbered 1-8 (excluding the transition metals)
-- The number of each group indicates how many valence electrons every element in the group has
-- Therefore, every element in the same column has the SAME NUMBER of valence electrons! (and therefore about the same reactivity)
-- Group 8 is known as the Noble Gases, which almost never react chemically
-- Group 1 is the Alkali Metals and Group 2 is the Alkaline Earth Metals, both are pretty reactive
-- Group 7 is known as the halogens, and they are also extremely reactive
Slide17 : Rows (Periods) The rows of the periodic table are called periods
Each period is numbered 1-7.
The number of each period corresponds to the valence energy level of all elements within that period.
***therefore by looking at the period and group of an element, you should know how many valence electrons it has and in what energy level they are