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Basic Chemistry copy

Key ideas needed to understand some basic chemistry for the Year 12 Biology course.
by Chris B on 10 July 2013

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Transcript of Basic Chemistry copy

Basic Chemistry
Matter
Elements
Atoms
Protons
Neutrons
Electrons
Symbols
Chemical reactions
Bonding
Ionic bonds
Covalent bonds
Double and triple bonds
Molecules
Polar Molecules
Hydrogen bonds
Water
Ions and Polar molecules dissolve in water
Acids
Bases
Neutral
pH
Occupies space
Has weight or mass
Can be broken down to elements
Can not be broken down by chemical reactions
Water is not an element
Oxygen and hydrogen are elements
Substance made up of two or more elements
Compounds
Atoms
Smallest particles of an element
Smallest particles of an element
There are 92 naturally occurring elements
96% of body weight of living organisms made up of Oxygen, carbon, Hydrogen and Nitrogen
positively charged particles in nucleus of atom
positively charged particles in nucleus of atom
positively charged particles in nucleus of atom
positively charged particles in nucleus of atom
Particles with no charge found in nucleus
Particles with negative charge found outside of nucleus
Electrons in an atom better represented as a cloud
Atomic number
Number of protons in an atom
All atoms of an element have the same atomic number
Atoms are neutral. # of protons = # of electrons
Atoms can vary in the number of neutrons they contain
Called isotopes
Isotopes of hydrogen
Electron shells
Electrons distributed around nucleus in layers called shells
Layer closest to nucleus has two electrons
Fill inner layers first
Outer shell may not contain the maximum number of electrons
This is the aluminium atom
It is showing three shells
Aluminium has three electrons in it's outer shell.
It may contain up to eight electrons in this shell.
Letters are used to represent atoms. The letters are called atomic symbols.
For example, the symbol for carbon is C.
The symbol for sodium is Na.
Atoms with incomplete shells react with others in a way that allows it to complete the outer shell.
Atoms react to give up, receive, or share electrons to produce a completed outer shell.
Chemical bonds form when atoms react to fill their outer shells with electrons.
A compound is two or more elements joined together by chemical bonds.
Ionic bonding occurs when electrons are transferred from one atom to another.
The transfer of electrons enables the atoms to have complete outer shells.
One electron in the outer shell
One electron MISSING in the outer shell
Extra electron transferred to the Chlorine atom
Sodium ion formed (+ve)
Chloride ion formed (-ve)
The electrical attraction between sodium ions (+) and chloride ions (-) produces the regular arrangement diagramed below.
Chloride ion in green
Sodium ion in grey
This forms the crystals of salt we know
Ionic bonds are weak and can be easily separated in water
Covalent bonds form when atoms share electrons.
Hydrogen atoms contain one electron and one proton
Below, two hydrogen atoms are bonded by a single covalent bond.
The two atoms each share a pair of electrons.
Molecules are two or more atoms that are held together by covalent bonds.
Molecules may be composed of atoms of the same element or of different elements.
Carbon needs four electrons, each hydrogen needs one
Each of the hydrogen atoms shares one electron with carbon
Simpler representation of methane
Even simpler: written as CH
4
Two covalently-bonded atoms will not share electrons equally.
The molecule will be polar
In the drawing below, hydrogen shares one pair of electrons with chlorine by a single covalent bond
The overall charge on the molecule is zero but chlorine has a partial negative charge and hydrogen has a partial positive charge
Hydrogen ion
Chloride ion
Shading is used in the drawing below to indicate the area of greatest electron density
As a result of this, the chloride ion is more negative than the hydrogen ion, which is relatively more positive.
Unequal sharing of electrons results in the oxygen having a partial negative charge and the hydrogen atoms having a partial positive charge.
The partial positive charge on the hydrogen atoms in a molecule will be attracted to atoms with a negative charge.
Forms a hydrogen bond
Hydrogen bonds are weak
Energy is required to form a covalent bond and energy is released when a Covalent bond is broken.
Hydrogen bonds
The partial positive charge on the hydrogen atoms in a molecule will be attracted to atoms with a negative charge.
Forms a hydrogen bond
Hydrogen bonds are weak
Water molecules are also attracted to other polar substances causing them to adhere to many kinds of materials
The attraction between water molecules and ions may be strong enough to separate the ions, causing the ions to become suspended (dissolved) in the water
Form when molecules are added to water and they lose a Hydrogen ion.
HCl
H
+
+
Cl
-
Acids produce hydrogen ions in water
Are substances that combine with hydrogen ions and reduce their concentration
NaOH
Na
+
+
OH
-
+
OH
-
H
H
2
O
+
Indirectly, NaOH reduces the amount of hydrogen ions
Water - produces equal amounts of hyrogen and hyroxide ions
Measures the concentration of hydrogen ions
Low pH (<7) = acids
High pH (>7) = bases
Neutral pH = 7
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5.
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Is formed when two or more atoms chemically combine to form a single species.
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