Chemistry lecture 4

Organic chemistry is the study of carbon compounds; biochemistry is the study of carbon compounds that wriggle.

Warm up

A Chemical is a Substance that: An organic chemist turns into a foul odor. An analytical chemist turns into a procedure. A physical chemist turns into a straight line. A biochemist turns into a helix. A chemical engineer turns into a profit.

Rules of the Lab

If an experiment works, something has gone wrong.

When you don't know what you're doing, do it neatly.

Always keep a record of your data. It indicates that you have been working.

Do not believe in miracles - rely on them.

Teamwork is essential, it allows you to blame someone else.

Any delicate and expensive piece of glassware will break before any use can be made of it.

Lecturer:D.Myagmarsuren.NUM

        

Atoms

                  We have already learned that ions are atoms that are either missing or have extra electrons. Let's say an atom is missing a neutron or has an extra neutron. That type of atom is called an isotope.

Isotopes are forms of a chemical element whose nuclei have the same atomic number, Z, but different atomic masses, A. The word isotope, meaning at the same place, comes from the fact that all isotopes of an element are located at the same place on the periodic table.

In science, a molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. A molecule consists of two or more atoms joined by shared pairs of electrons in a chemical bond. It may consist of atoms of the same chemical element, as with oxygen (O₂), or of different elements, as with water (H₂O). Abstractly, a single atom may be considered a molecule, as it is when referred to collectively with molecules of multiple atoms, but in practice the use of the word molecule is usually confined to chemical compounds, of multiple atoms.

Mole (unit)

The mole (symbol: mol) is one of the seven SI base units and is commonly used in chemistry. It measures the amount of substance of a system and is defined as the amount of substance that contains as many elementary entities as there are atoms in exactly 0.012 kilogram of carbon-12. This quantity is known as Avogadro's number and is approximately 6.0221415 × 10²³ (2002 CODATA value).

Because of the relationship of the atomic mass unit to Avogadro's number, a practical way of stating this for atoms or molecules is: That volume of the substance containing exactly the same number of grams as the number of the atomic weight of the substance. Since iron, for example, has an atomic weight of 55.845, there are 55.845 grams (0.055845 kilograms) in a mole of iron.

While the atoms may have different masses and organization, they are all built with the same parts. Electrons, protons, and neutrons make the Universe the way it is.

You could start really small...
- Particles of matter
- Atoms
- Molecules
- Macromolecules
- Cell organelles
- Cells
- Tissues
- Organs
- Systems
- Organisms
- Populations
- Ecosystems
- Biospheres
- Planets
- Planetary Systems with Stars
- Galaxies
- The Universe
...And finish really big.

Wow. All of that is possible because of atoms.

Mixtures and pure substances

Matter, that is everything you can see, taste, and touch, is made of different kinds of atoms, i.e. elements. Matter can be classified into two categories: mixtures and pure substances.A pure substance can be either a compound or an element. Some pure substances are made of only one kind of atom. However, pure substances can also contain more than one kind of atom. if it contains only one kind of molecule. Pure water, for example, contains two different elements; hydrogen and oxygen in the form of water molecules.  Pure ammonia contains three hydrogen atoms and one nitrogen atom in ammonia molecules, and pure carbon dioxide contains two oxygen atoms and one carbon atom in carbon dioxide moleculses.  Even though they contain more than one kind of atom, these are considered to be pure substances because they have only one kind of molecule.   We call such pure substances compounds.  In general, a compound is two or more atoms bonded together in a fixed ratio (e.g. there is always one oxygen atom to two hydrogen atoms in a water molecule for a ratio of two to one.).  Because the atoms in compounds have a fixed ratio, they are also considered pure substances. Matter can also exist in mixtures.  A mixture is defined as two or more elements physically (but not chemically) combined.  The air we breath is a mixture of nitrogen gas and oxygen gas (and other trace substances). Tap water is a mixture of water molecules and small amounts of metals and chlorine.  Unlike a compound, the components of a mixture are not fixed and can vary.  Therefore, mixtures are not pure substances.