Physics notes

• What is an Element?

  A chemical element is a chemical substance that cannot be broken down into other substances by chemical reactions. The basic particle that constitutes a chemical element is the atom. Chemical elements are identified by the number of protons in the nucleus of their atoms, known as the element's atomic number.
• WHAT IS AN ATOM?

  The atom is the basic particle of the chemical elements. An atom consists of a nucleus of protons and generally neutrons, surrounded by an electromagnetically-bound swarm of electrons.
• GROUPS AND PERIODS OF THE PERIODIC TABLE

  The columns of the periodic table are called GROUPS. Members of the same group in the table have the same number of electrons in the outermost shells of their atoms and form bonds of the same type.

  The horizontal rows are called PERIODS. Periods correspond to the relationship of orbitals, or likely areas in which electrons will be found, inside the outermost shell of the atom.
• THE FAMILIES OF THE PERIODIC TABLE


  METALS ARE ON THE LEFT HAND SIDE AND NON-METALS ON THE RIGHT
• Alkali Metals (Group I)


  • Very reactive metals that do not occur freely in nature
  • Malleable, ductile, good conductors of heat and electricity
  • Can explode if they are exposed to water
• Alkaline Earth Metals (Group II)


  • Metals
  • Very reactive (less than Alkali metals)
  • Harder, denser than group 1
  • Not found free in nature
• Halogens (Group VII)


  • "Halogen" means "salt-former" and compounds containing halogens are called "salts"
  • Exist in all three states of matter
• Noble Gases (Group VIII)

  • Do not form compounds easily
• Inert Elements


  Have full outer shells
• THE PROPERTIES OF METALS AND NON-METALS

  Metals and non-metals have distinct properties. That means their properties are unique and different from each other. 

  The properties of semi-metals

  Some elements are not quite metals, but they are not quite non-metals either. They just don't fit into either category!
•  

  Metal

  Metallic Luster

  Good conductors of heat and electricity

  Malleable and Ductile

  High Melting Point

  Mostly solid at room temperature

   

  Non Metal

  Dull

  Poor conductors of heat and electricity

  Brittle

  High Melting Point

  Often liquids or gases at room temperature
• DALTON’S 5 CLAIMS ABOUT ELEMENTS AND ATOMS

  1.  Each element consists of indivisible, minute particles called atoms.
  2.  All atoms of a given element are identical.
  3.  Atoms of different elements have different masses.
  4. Atoms can neither be created nor destroyed during chemical reactions .
  5. Atoms chemically combine in fixed ratios to form compounds.
• Electronegativity


  The tendency of an atom to attract electrons in a molecule
• Electronegativity on the periodic table


  • Generally increases as you move from left to right across a period
  • Decreases as you move down a group
• Degree to which an atom attracts electrons in a chemical bond


  Described by electronegativity
• Difference in electronegativity greater than 1.7

  Bond character is ionic (a complete transfer of the electron)
• Difference in electronegativity between 0.4 and 1.7

  Bond character is polar covalent (a sharing of the electron)
• WHAT IS THE OXIDATION NUMBER OF AN ELEMENT?

  The oxidation number is a number assigned to elements to show how many electrons were lost or gained. A positive number means electrons were lost. A negative number means electrons were gained.
• WHAT IS AN IONIC BOND?


  Ionic bonding is the complete transfer of valence electron(s) between atoms. It is a type of chemical bond that generates two oppositely charged ions. In ionic bonds, the metal loses electrons to become a positively charged cation, whereas the nonmetal accepts those electrons to become a negatively charged anion. (between a metal and a non-metal)
• WHAT IS A COVALENT BOND?

  A chemical bond formed when electrons are shared between two atoms. Usually each atom contributes one electron to form a pair of electrons that are shared by both atoms. (between a non-metal and a non-metal or metalloid)
• Atom


  Smallest unit of an element that has the chemical properties of that element
• Most atoms don't ride solo, instead they bond with other atoms
• Ionic bond


  Attraction between oppositely charged ions formed when one atom completely transfers one or more electrons to another atom
• Ionic bond


  • Table salt (sodium chloride)
• Formation of ionic bond in sodium chloride


  1. Sodium atom gives up one electron to chlorine atom

  2. Ions are formed

  3. Ions arrange in a 3D grid (lattice)

  4. Each sodium ion bonded to six chloride ions, each chloride ion bonded to six sodium ions
• Covalent bond


  Atoms share electrons, each atom attracted to the shared electrons between them
• Covalent bonds


  • Proteins
  • DNA
• Covalent bonding


  • Atoms can covalently bond with just one other atom or with many more
  • Number of other atoms an atom can bond with depends on how its electrons are arranged
• Every atom of a pure, unbonded element is electrically neutral because it contains the same number of protons in the nucleus as it does electrons around the nucleus
• Only the outermost electrons, the ones in orbitals furthest from the nucleus, the ones with the most energy, participate in bonding
• Number of bonds atoms can form


  • Carbon can form four bonds
  • Nitrogen can form three bonds
  • Oxygen can form two bonds
  • Hydrogen can only form one bond
• Molecule


  Groups of atoms that share electrons covalently with each other
• Molecules


  • Oxygen gas (two oxygen atoms)
  • Human chromosome 13 (over 37 billion atoms)
• This neighborhood, this city of atoms, is held together by the humble chemical bond
• WHAT IS A CHEMICAL REACTION?

  Chemical reactions are the processes by which chemicals interact (REACTANTS) to form new chemicals with different compositions (PRODUCTS). Simply stated, a chemical reaction is the process where reactants are transformed into products.
• THE TABLE SALT REACTION (IONIC BOND)

  • An electron is donated by the Sodium atom to the Chlorine atom.
  • The Sodium atom now has a positive charge (Na+) and is a Sodium ion as it has more protons than electrons.
  • The Chlorine atom now has a negative charge (Cl-) and is a Chloride ion as it has more electrons than protons.
  • The opposite charges of the two ionic atoms pulls them together and the ionic bond is created. (electrostatic forces)
• COVALENT BOND IN WATER

  • The Hydrogen atom and the Oxygen atom share an electron pair.
  • The water molecule is polar in nature due to its shape
  • Hydrogen bonds form between neighboring hydrogen and oxygen atoms of adjacent water molecules
• THE WATER EQUATION

  A balance equation needs to have the same number of atoms of all the elements on either side of the equation.
• THE SALT EQUATION

  A balance equation needs to have the same number of atoms of all the elements on either side of the equation.
• Over time, our knowledge about the elements and their behavior increased and scientists recognised the need to organise this information