Chemistry the Essential Element

Atoms elements and their behavior

Chemistry Concept Review

Atomic Mass V.S. Atomic #• There is a difference between the meanings of atomic mass and mass number. One is

the average weight of an element and the other is the total number of nucleons in the atom's nucleus.

• Atomic mass is also known as atomic weight. Atomic mass is the weighted average mass of an atom of an element based on the relative natural abundance of that element's isotopes.

• Mass number is a count of the total number of protons and neutrons in an atom's nucleus.

Example:Hydrogen has three natural isotopes: 1H, 2H, and 3H. Each isotope has a different mass number.

• 1H has 1 proton. Its mass number is 1. 2H has 1 proton and 1 neutron. Its mass number is 2. 3H has 1 proton and 2 neutrons. Its mass number is 3.

• 99.98% of all hydrogen is 1H 0.018% of all hydrogen is 2H 0.002% of all hydrogen is 3H Together, they give a value of atomic mass of hydrogen equal to 1.0079 g/mol.

How to find # of neutrons?• Remember the formula. To find the

number of neutrons in the future, simply use this formula:

# of neutrons = atomic mass - atomic number

How do I find # of protons?• The atomic number is the number of

protons in an atom of an element.

Ex: krypton's atomic number is 36. This tells us that an atom of krypton has 36 protons in its nucleus. every atom of krypton contains 36 protons. If an atom doesn't have 36 protons, it can't be an atom of krypton.

How do I find # of electrons?• By definition, atoms have no overall

electrical charge. There must be a balance between the positively charged protons and the negatively charged electrons.

• Atoms must have equal numbers of protons and electrons. An atom of krypton must contain 36 electrons since it contains 36 protons.

What is an ion?• Ion-An atom or molecule with a net electric charge due to

the loss or gain of one or more electrons.

• An atom can gain or lose electrons, becoming what is known as an ion. An ion is nothing more than an electrically charged atom. Adding or removing electrons from an atom does not change which element it is, just its net charge.

• For example, removing an electron from an atom of krypton forms a krypton ion, which is usually written as Kr+. It is positively charged because a negatively charged electron was removed from the atom.

Neutral, Negative, Positive

In SummaryFor any element:

• Number of Protons = Atomic Number• Number of Electrons = Number of Protons = Atomic

Number• Number of Neutrons = Mass Number - Atomic Number

For krypton:

• Number of Protons = Atomic Number = 36• Number of Electrons = Number of Protons = Atomic

Number = 36• Number of Neutrons = Mass Number - Atomic Number = 84 - 36 = 48

Mixture v.s. Compound: What is the difference?

Mixtures

• Mixtures are impure substances.

• They are made up of two or more substances mixed physically.

• The constituents of a mixture are present in varying ratios.

• Mixtures do not have fixed properties. Their properties depend on the nature of their components and the ratios in which they are combined.

• In mixtures, no new substance is formed. The properties of a mixture are the same as the properties of its constituents.

• The constituents of a mixture can be separated easily by physical methods.

DO NOT WRITE THIS DOWN

Mixtures 2• Individual molecules or parts not

chemically reacting with each other

• When you see distilled water (H2O), it's a pure substance. That means that there are only water molecules in the liquid.

Mixtures 3• Solutions are also mixtures, but all of the

molecules are evenly spread out through the system. They are called homogenous mixtures.

• A heterogeneous mixture does not have a definite composition. Although you may add one substance to the other, they will stay separate in the mixture. We say that these heterogeneous mixtures are non-uniform,

in other words they are not exactly the same throughout.

Mixture TypesHomo= same Hetero= different

Watch video on how to make a distiller

• http://illinois.pbslearningmedia.org/resource/ess05.sci.ess.watcyc.solarstill1/solar-still-part-i-salt-water/

• How a water treatment plant works• http://www.teachersdomain.org/asset/ate1

0_vid_watertreatment/

Mixtures Pt 4: Alloys• Alloys are basically a mixture of two or more metals. Don't forget

that there are many elements on the periodic table. Elements like calcium (Ca) and potassium (K) are considered metals. Of course, there are also metals like silver (Ag) and gold (Au). You can also have alloys that include small amounts of non-metallic elements like carbon (C). Metals are the key thing to remember for alloys.

• The combinations of metals work better together than any of the metals do alone. Metallurgists (people who work with metals) sometimes add chromium (Cr) and/or nickel

(Ni) to steel. While steel is already an alloy that is a very strong metal, the addition of small amounts of the other metals help steel resist rusting

Compounds• Compounds are groups of two or more elements

that are bonded together.

• Molecule is the general term used to describe atoms connected by chemical bonds. Every combination of atoms is a molecule. Compounds happen with atoms from different elements.

• Not all molecules are compounds because sometimes the atoms are of the same element. Hydrogen gas (H2) is a good example of a molecule that is not a compound. 

Characteristics of Compounds

• Compounds are pure substances.• They are made up of two or more elements

combined chemically.• The constituents of a compound are present in a

fixed ratio.• Compounds have fixed properties. • A compound can have properties different from its

elements, as a new substance is formed when the elements are chemically combined.

• The elements of a compound can be separated only by chemical methods.

Hydrogen Element and Water Molecule

Hydrogen ElementWater Molecule

Ionic Bonds• An ionic bond is a type of chemical bond formed

through an attraction between two oppositely charged ions.

• Ionic bonds are formed due to the attraction between an atom that has lost one or more electron (known as a cation) and an atom that has gained one or more electrons (known as an anion).

• Usually, the cation is a metal atom and the anion is a nonmetal atom.

• Common table salt is sodium chloride. When sodium (Na) and chlorine (Cl) are combined, the sodium atoms each lose an electron, forming cations (Na+)

• The chlorine atoms each gain an electron to form anions (Cl−). Na + Cl → Na+ + Cl− → NaCl

Ionic Bond Visual

Ionic Bonds Cont.

Difference Between Covalent and Ionic Bond

Ionic Bond Animation• <iframe width="420" height="315"

src="//www.youtube.com/embed/xTx_DWboEVs" frameborder="0" allowfullscreen></iframe>

Covalent Bonds• Covalent Bonds: a chemical bond that

involves sharing a pair of electrons between atoms in a molecule.

Covalent Bonds

Covalent Bonds

Covalent Bonds

Covalent Bonds

http://youtu.be/1wpDicW_MQQ- Covalent Bond Animation

Covalent vs. Ionic• http://youtu.be/QqjcCvzWwww- Simple

explanation of Covalent v.s. Ionic

• Detailed/ Long Video about Ionic and Covalent Bonds and polarity

http://www.youtube.com/watch?v=7DjsD7Hcd9U

Mixture, Elements, Compounds

Chemically Separable ?

Chemical Reactions: Explosive Possibilities

Chemical Reactions• http://youtu.be/b4wveY2-lCo

Funny animation

Balancing Chemical Equations