C4 Flashcards
Describe briefly the structure of an atom.
- Central nucleus surrounded by shells of negatively charged electrons
- Electrons drawn as crosses on the orbitals
- Nucleus is made up of protons and neutrons
- Nucleus is positively charged
- An atom has no overall charge because it has the same amount of protons and electrons so the charges cancel out
Describe the history of the atom, with reference to John Dalton, J. J. Thomson and Ernest Rutherford’s theories.
1800’s - John Dalton said that atoms of the same element were the same
1890’s - J. J. Thomson discovered the electron
1911 - Ernest Rutherford discovered that the atom had. Dense centre called the nucleus
1913 - Neils Bohr predicted that electrons occupy orbitals
Define: element
• An element is made of one type of atom. They cannot be broken down. There are just over 100 naturally occurring elements in the periodic table
Define: compound
• A substance made of two or more elements that are chemically combined. You can identify the elements within the compound from the formula.
What is the mass number?
• Total number of protons and neutrons
What is the atomic number?
• (or the proton number) is the number of protons in an atom
What can the group (column) and period (row) number tell you about an element’s atom?
- Group number = same as the number of electrons in the outer shell
- Period number = same as the number of occupied shells (that contain electrons
What is an isotope?
- Atoms of the same element that have the same atomic number but different mass number
- For example, more or less neutrons with the same number of protons and electrons
Describe the three different types of bonding.
- Ionic bonding - between non-metals and metals
- Covalent bonding - between non-metals
- Metallic bonding - for metals only
What is an ionic bond?
- When a metal and a non-metal combine, electrons are transferred from one atom to the other forming ions
- Each ion will have a complete outer shell (a stable octet)
What is a covalent bond?
- Between non-metals
- They share PAIRS of electrons
- Covalently bonded compounds include water H20 and carbon dioxide CO2
What do simple covalently bonded molecules e.g. water and. Rabin dioxide have?
- Weak intermolecular forces
- Consequently they have low melting points
- Also can’t conduct electricity because there are no free electrons
How was first to suggest the ‘Law of Triads’ to group the elements?
- Dobereiner
- Grouped elements into sets of three with similar properties
- Middle element would have the arp enrage mass of the other two elements
- However, not all elements were known and pattern did not always work
Who was first scientist to make a table of elements?
- John Newlands
- Called the table the ‘Law do Octaves’
- Every eighth element behaved the same
- However, included some compounds which he believed to be elements
Who is the the author of the modern periodic table?
- Mendeleev
- Left gaps in his table for unknown elements
- Made predictions for unknown elements properties
- These predictions were later proven correct
- Also, investigations on atomic structure agreed with his ideas
