Topic one

• John Dalton's atomic theory:

  • Matter is made of atoms that are tiny particles that cannot be created, destroyed, or divided
  • Atoms of the same element are identical, while atoms of different elements are different
  • Different atoms combine to form new substances
• Discovery of the electron by J.J. Thomson in 1897:

  • Identified the electron as a negatively charged subatomic particle
  • Proposed the plum pudding model of the atom with negative electrons spread throughout soft globules of positively charged material
• Ernest Rutherford's model of the atom based on the gold foil experiment in 1909:

  • Discovered the nucleus as the central region of the atom where most of the mass is concentrated
  • Proposed the nuclear model of the atom with electrons orbiting around the nucleus
• Niels Bohr's model of the atom in 1913:

  • Proposed that electrons orbit the nucleus in fixed shells or orbitals at set distances
  • Each orbital has a different energy associated with it, with higher energy orbitals located further away from the nucleus
• Discovery of the neutron in 1932 by James Chadwick:

  • Neutrons are large, neutral particles within the nucleus
  • Neutrons were discovered based on differences between atomic mass and atomic number
• Atoms are made of protons, neutrons, and electrons:

  • Protons and neutrons are in the nucleus, while electrons orbit around the nucleus
  • The mass of an atom is concentrated in the nucleus, which is positively charged due to the protons
• Atomic Structure Key Terms:

  • Atomic number: number of protons in the nucleus of an atom
  • Mass number: sum of the number of protons and neutrons in the nucleus of an atom
  • Nucleon number: alternative term for mass number, representing protons and neutrons collectively

  
• Conventions for showing atomic number and mass number:

  • Mass number usually written as a superscript
  • Atomic number usually written as a subscript
• Isotopes are atoms of the same element that contain the same number of protons and electrons but a different number of neutrons
• Isotopes have the same chemical characteristics due to having the same number of electrons in their outer shells
• To find the number of protons, electrons, and neutrons in an atom:

  • Number of protons = atomic number
  • Number of neutrons = mass number - number of protons
  • Number of electrons = number of protons (since atoms are neutral)
• Relative atomic mass is calculated from the mass number and relative abundances of all the isotopes of an element
• Mendeleev's Periodic Table:

  • Organized elements into vertical columns based on properties and compounds
  • Arranged elements horizontally by increasing atomic mass
  • Left gaps for undiscovered elements, predicting their properties based on neighboring elements
• Mendeleev's Arrangement:

  • Before the discovery of subatomic particles, scientists struggled to find ways of ordering elements and their chemistry
  • Elements sorted by mass into a table revealed patterns at regular periods, leading to the term periodic
  • Mendeleev organized elements into vertical columns based on their properties and compounds, then horizontally by increasing atomic mass, noticing chemically similar elements fell into the same columns
• An ion is an electrically charged atom or group of atoms formed by the loss or gain of electrons

  
• Mendeleev's Periodic Table showed gaps where elements didn't fit the pattern when arranged by atomic mass

  • Mendeleev left gaps in the table for undiscovered elements, predicting their properties based on the properties of neighboring elements
• Negative ions are called anions and form when atoms gain electrons, meaning they have more electrons than protons
• Mendeleev predicted elements with the same properties should be placed in the same column, using gaps in the table to predict properties of undiscovered elements
• Mendeleev's table allowed him to predict the existence and properties of then-unknown elements by leaving gaps to be filled by later-discovered elements
• All metals lose electrons to other atoms to become positively charged ions
• All non-metals gain electrons from other atoms to become negatively charged ions
• Ions have a different number of electrons to the number of protons, depending on their charge
• A positively charged ion has lost electrons and therefore has fewer electrons than protons
• Problems with Mendeleev's Table:

  • Isotopes were unknown in Mendeleev's time, leading to some inaccuracies in his work
  • Mendeleev switched the order of tellurium and iodine in his table due to chemical properties, a problem unsolved in his lifetime
  • The discovery of the proton led to the determination of atomic number, used in the modern periodic table which fits with Mendeleev's patterns
• The Modern Periodic Table:

  • Over 100 chemical elements arranged by increasing atomic number, with each element having one more proton than the preceding one
  • Elements are grouped in columns with similar properties and in rows showing the number of electron shells, numbered from 1 to 7
• An atom consists of a nucleus containing protons and neutrons, with electrons orbiting the nucleus in shells where each shell can hold a specific number of electrons

  
• Group: Vertical columns in the periodic table that show how many outer electrons each atom has, numbered from 1 – 7, with a final group called group 0 (instead of group 8)
• In an atom, the nucleus contains positively charged protons, while the negatively charged electrons orbit around it

  
• Group 4 elements have atoms with 4 electrons in the outermost shell, while group 6 elements have atoms with 6 electrons in the outermost shell
• The nucleus of an atom, where the mass is concentrated, is made up of protons (positively charged) and neutrons (neutral), while electrons (negatively charged) orbit the nucleus

  
• Metals further to the left on the periodic table do not have many electrons to remove from their outer shells
• As you descend the groups, the outer shell electrons become further away from the nucleus due to increasing atomic size, weakening their attraction to the nucleus
• Table showing the relative mass and charge of protons, neutrons, and electrons

  
• Non-metals on the right-hand side of the periodic table have a lot of outer electrons, making it more feasible for them to gain (or share electrons) to obtain a full outer shell
• The atomic number is unique to each element and remains constant during chemical reactions
• The atomic number of an element is the number of protons in the nucleus, while the mass number is the sum of the number of protons and neutrons in the nucleus

  
• In atoms, the outermost shell is called the valence shell, and atoms react with other atoms to achieve a full outer shell for stability
• Diagram of an atom showing electron shells and the number of electrons each shell can accommodate

  
• Electronic configurations can be represented by writing the number of electrons in each electron shell, separated by full stops
• Table showing the element, atomic number, and electronic configuration of the first 20 elements