Structure and Properties of Atoms and Molecules

Classified in Chemistry

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  1. Structure of an atom -  An atom is composed of protons, electrons, and neutrons. The entire mass of an atom is concentrated in the nucleus which is at the centre.

    1. Protons - Protons are the positively charged particles which are present in the nucleus of an atom.

    2. Neutrons - Neutrons are the particles in an atom that have a neutral charge. 

    3. Electrons - An electron is a negatively charged subatomic particle that can be either bound to an atom or free

    4. Atomic Mass (what it represents) - The atomic number refers to the number of protons in the atom's nucleus, 

    5. Atomic Number (what it represents) - The atomic mass of an element represent the average total mass of its neutrons, protons, and electrons

  2. Standard Atomic Notation

    1. How to determine how many neutrons, protons and electrons an atom has - The number of electrons in a neutral atom is equal to the number of protons. The number of neutrons is equal to the division/difference between the mass number of the atom (M) and the atomic number/number of protons (Z).

    2. How to determine an atom’s atomic mass - mass number = protons + neutrons. If you want to calculate how many neutrons an atom has, you can simply subtract the number of protons, or atomic number, from the mass number.

  3. How to draw a Bohr-Rutherford Diagram g7IWoumrs9_sRKMmfW8mY-JTqBCPBWXeHaK7lBK_A-jd4JAMZ9O1wikpF5w_z5fw_4EQolQadrLThjlVhlLvvQRklXk4Sj0AL3LCARObOMoJ8h6JXlrtZ3T6SAyfaKL_dHRp8Z47zg0oc2UAiuMkDck

  4. What is an ion - an atom or molecule with a net electric charge due to the loss or gain of one or more electrons.

    1. Cations are ions that are positively charged. 

    2. Anions are ions that are negatively charged. Ions are charged atoms or molecules.

 If a balanced atom loses one or more electrons, it will become a positively charged cation. If a balanced atom gains one or more electrons, it will become a negatively charged anion.

  1. Four families on the periodic table and how many valence electrons they each have

    1. Alkali metals - Group 1 (IA) - 1 valence electron.

In their pure forms, the alkali metals (lithium, sodium, potassium, rubidium, and cesium) are soft, shiny metals with low melting points. Alkali metals react readily with air and moisture. 

  1. High reactive metals.

  2. Not found freely in nature.

  3. Stored in a mineral oil solution.

  4. Low melting points.

  5. Low densities (lower than other metals)

  6. Low electronegativity.

  7. Low ionization energy.

  8. React easily with halogens.

  1. Alkaline earth metals - Group 2 (IIA) - 2 valence electrons. 

beryllium, magnesium, calcium, strontium, barium, and radium.

  1. Alkaline earth metals have two valence electrons.

  2. They have low ionization energy, low electron affinity, and low electronegativity.

  3. They are highly reactive and often form divalent cations.

  4. They are good conductors of electricity.

    1. Halogens - Group 7A (or VIIA) - 7 valence electrons

 a chemical element that forms a salt when it reacts with metal. Halogen lamps are illuminated by bulbs that contain a halogen and an inert gas. There are five halogens in the periodic table of chemical elements: fluorine, chlorine, bromine, iodine, and astatine.

  1. They all form acids when combined with hydrogen.

  2. They are all fairly toxic.

  3. They readily combine with metals to form salts.

  4. They have seven valence electrons in their outer shell.

  5. They are highly reactive and electronegative.

    1. Noble gasses - Group 18 (VIIIa) - 8 valence electrons

any of the gaseous elements helium, neon, argon, krypton, xenon, and radon, occupying of the periodic table

Noble gases are odorless, colorless, nonflammable, and monatomic gasses that have low chemical reactivity. The full valence electron shells of these atoms make noble gasses extremely stable and unlikely to form chemical bonds because they have little tendency to gain or lose electrons.

  1. Ionic bonds - Ionic bonding is a form of chemical connection in which one atom loses valence electrons and gains them from another.  Ionic bonds result from the attraction between oppositely charged ions. For example, sodium cations (positively charged ions) and chlorine anions (negatively charged ions) are connected via ionic bonds in sodium chloride, or table salt. Ionic compounds generally form from metals and nonmetals

One type of chemical bond is an ionic bond. Ionic bonds result from the attraction between oppositely charged ions.

  1. Ionic compounds - 

NaCl, sodium chloride

ordinary table salt

NaF, sodium fluoride

ingredient in toothpaste

NaHCO3, sodium bicarbonate

baking soda; used in cooking (and as antacid)

Na2CO3, sodium carbonate

washing soda; used in cleaning agents

  1. + Molecular bonds - molecular bond, is a chemical bond formed between two atoms that share a pair of electrons; the elements that form these bonds are generally non-metals.


  1.  Molecular compounds -water (H2O) and carbon dioxide (CO2)

    1. What they are (i.E. Metal + non-metal / two non-metals)SGSL-AzSV_SYzIK_BTZuNMX_t8_xVQHuVLG_W6DMLJ3CIIC7mrHZSboZMr8sXg4HFwKQ1vV2lSWqpI0AJVS11eB5zO2hZEOezBBVWw1sEN9_1_D-QZyxgVHuVz8zt0FIA8v5yBoYr5s2mdVFjUCPu1Q

    2. ZALoKsw7fMVczA6dbEViumHnD4V3e67ClVB7pbVUe2zvauBIAP-Az9S-n96Npgfnd8AIhLJV24oZ5pk__MwmuLXAsnbRWDLCx844trTRgz82QILO7p86ArYxEQm9CkHIrHgDma9B0G9jNT8ACKDwxmU




  1. How to name them

  2. How to write the formula


Metals have 1,2 or 3 valence electrons so they always ionize by losing electrons while non metals have 4, 5, 6 or 7 valence electrons so they ionize by gaining electrons.

Alkali metals have one valence electron, whereas alkaline earth metals have two valence electrons. Alkali metals possess a low melting point, whereas alkaline earth metals possess' high melting point. Alkali metals posse's lower ionization energy, whereas alkaline earth metals posse's greater ionization energy.

The ratio of the numbers of atoms that can be bonded together to form molecules is fixed; for example, every water molecule contains two atoms of hydrogen and one atom of oxygen.

Atoms like these are called "ions." These two oppositely-charged ions are then drawn together and held by a force similar to magnetism. We say that the ions are held together by an "ion bond." Substances made up of ions are called "ionic compounds." An example of an ionic compound would be table salt.

The chemical reactivity of an atom is mainly determined by valence electrons. Atoms which have a complete shell of valence electrons tend to be chemically inert. Atoms with one or two valence electrons are highly reactive.




Sulphur dioxide SO2

Nitrogen trioxide NO3

Phosphorus pentachloride PhCl5

Dinitrogen tetroxide N2O4

Carbon dioxide CaO2

Carbon monoxide CaO

Carbon trioxide CaO3

Sulphur pentoxide SO5

Nitrogen tribromide NBr3

Dinitrogen pentoxide N2O5

Oxygen difluoride Of2


Sodium chloride Na+Cl-

Magnesium oxide Mg2+O2-

Magnesium chloride MgCl2

Sodium oxide Na2o

Lithium bromide LiBr

Aluminum fluoride AlF3

Sodium nitride Na3N

Potassium fluoride KF

Calcium sulphide CaF2

Calcium bromide CaBr2

Aluminum oxide Al2O3

Calcium nitride CaN2

Aluminum nitride AlN

Lithium nitride Li3N

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