Atomic Structure - Chemistry

relative mass relative charge location

proton 1 +1 in nucleus

neutron 1 0 in nucleus

electron 1/2000 -1 orbiting nucleus on shell


  • relative atomic mass → on top; average number of protons & neutrons in an element

  • atomic number → on bottom; unique to each element; number of protons in an atom of that element

  • number of neutrons → mass number - atomic number

  • number of electrons → number of protons (if atom neutral)

  • all substances made of atoms; has a radius of 0.1nm (1x10-⁹m)

  • atoms have small central nucleus made of positive particles, protons, and neutral particles, neutrons

  • around nucleus there are negative electrons


Elements and Compounds

  • element → substance made from just 1 type of atom, can be found in the periodic table; e.g gold, oxygen

  • compound → two or more different atoms chemically bonded together; e.g water, carbon dioxide

  • mixture → two or more elements and/or compounds not chemically bonded together


Isotopes

  • Isotopes → atoms of same element that have same number of protons but different number of neutrons e.g, Chlorine; have nearly the same chemical properties but different physical properties


Electronic structure of atom

  • electrons in atoms occupy energy levels; outside nucleus → different shells can hold different maximum numbers of electrons

  • electron in atom occupies lowest energy first; shell nearest to nucleus → when this shell full, electrons begin to occupy next shell (energy level)

  • 1st shell holds 2 electrons

  • 2nd shell holds 8 electrons

  • 3rd shell holds 8 electrons

  • 4th shell holds 2 electrons

  • number of outer shell electrons that an element has is same as group number

  • noble gases (group 8/0) have full outer shells of electrons → makes them stable + unreactive


Scientific Models

  • scientific model → simple system that helps us to understand a more complex system

  • Democritus's theory (500BC)→ small invisible, indivisible, indestructable particles; many different types; empty space in between atoms

  • the plum pudding model (1897)→ J.J Thomson; discovered electrons; electrons randomly embedded in positive 'batter’

  • Rutherford and Marsden (1911) → shot alpha partide at gold leaf (alpha particles positive) expected all of them to go through, most went through, some deflected & reflected; theorised atoms mostly empty space; positive thing in middle as similar things repel

  • Neils Bohr (1911-1932) → suggested electrons revolve around nucleus in stable orbits (shells); futher experimen led to idea that positive charge in nucleus due to tiny particles called protons

  • James Chadwick (1932) → discovered new particle inside nucleus called neutron


Ionic and Covalent Bondings & Compounds

  • chemical bonding involves either losing or sharing electrons from outer shell of electrons of atoms in order to gain noble gas electronic structure

  • compounds formed from metals & non-metals made of ions

  • metals Iose elections to form positive ions

  • non-metals gain electrons to form negative ions

  • ionic bonding → when a metal forms a bond with a non metal; involves transfer of electrons

  • ionic compounds → great structure of ions; held together by strong electrostatic forces of attraction between oppositely charged ions ; act in all directions in the lattice

  • lattice → repeating structure of positivity & negatively charged ions; extending in all directions

  • ionic compounds have high melting + boiling points, large amounts of energy needed to break the strong bonds

  • if ionic compound melted/dissolved in water, will conduct electricity, ions free to move & carry charge

  • convalent bonding → when two non-metals bond involves sharing of electrons


Metallic Structures & Bonding

  • metalic structure → repeating pattern of positive metal ions, surrounded by delocalised electrons; held together by strong electrostatic forces of attraction between delocalised elections & positive metal ions, extends in all directions

  • metals consist of giant lattice of atoms arranged in regular pattern; outer shell electrons from each atom delocalised, free to more throughout whole structure

  • metallic bond → strong electrostatic force of attraction between positive nucleus + delocalised electrons


Properties of metals

  • metals have high melting & boiling point → large amount of energy required to overcome strong electrostatic force

  • metals good electricity conductor → delocalised electron able to more through structure and carry charge

  • metals good thermal conductor→ thermal energy transferred by delocalised electrons

  • metals are malleable (can be bent & hammered into different shapes) → all ions same size, forms layers, can slip & slide over each other while maintaining metallic bonding

  • metals are sonorous → make sound when hit