chapter 2 Flashcards
3 points of rutherfords atomic theory
- Most of an atoms mass and positive charge are centered in the nucleus
- Most of the volume of the atom is empty, with electrons dispersed throughout
- There are as many changed atoms outside of the nucleus as there are protons. The atom is electrically neutral
problems with rutherfords model
atoms weigh more than they should with only protons
Their mass is due to neutrons, particles similar to protons but no electrical charge
modern atomic theory on electrons and the nucleus
- Electrons: much smaller than protons or neutrons, make up most of volume of atom, lots of space between them, and are located in orbitals.
- Nucleus: contains protons and neutrons, dense, and most of the mass of the atom
what is each element determined by? what yields the mass number?
- • Each element is determined by the number of protons in the nucleus - atomic number (Z)
- • The total number of protons and neutrons yields the mass number (A)
- • Each element is represented by a one or two-letter symbol
what is an isotope?
atoms that have the same number of protons but different number of neutrons and different mass numbers.
what is atomic mass? used for?
average weighted mass
• We can use the atomic number to identify what element it is
how do we determine atomic mass?
• (this is percent composition) Average Atomic mass= sum of (Isotopic mass) X (Fractional abundance)
how is the atomic number (Z) affected by isotopes? mass number (A)?
- Atomic number (Z) for isotopes remains constant, while mass number (A) can vary
- Only Z and chemical symbol can identify an element
what is A made of? Z?
- A=#p+ + #n0
* Z=#p+
what is the standard reference for atomic mass units?
- 12C - standard reference for atomic mass units (absolute value bc. Infinite zeros)
- All other atomic masses are quoted/measured relative to this standard mass
why is the mole used? what is avogadros number?
cientists use the mole to count atoms
• A mole contains 6.02214 x 10^23 which is known as Avogadro’s number (NA) (on data sheet)
how was avogadros number decided on?
- Was decided on bc the value of a mole is the number of atoms in exactly 12 grams of carbon-12
- Therefore, 1 mol C atoms = NA
how does a mole relate to atoms?
- Mole gives us the relationship between mass and the number of atoms
- If we can weigh a substance/element, we can count how many atoms are present
- Ex: how many atoms are in 3.5 mol of silver?
how is the periodic table arranged?
- Dmitri Mendeleev arranged the elements consisting of a series of rows and columns
- Arranged in elements with similar properties into columns
- He was able to predict the presence of as of yet undiscovered elements
what does periodic law state?
• The periodic law states that the chemical properties of the elements are dependent on their atomic numbers
why do electrons intermingle with atoms?
• Because the space where electrons occupies a large percentage of an atoms volume, it is electrons which “intermingle” with other atoms. Producing chemical reactions
what gives an atom its chemical properties?
where are electrons found?
• The number and arrangement of the electrons give an atom its chemical properties. • Electrons are generally found in discrete energy shelves, called orbitals
what is the outer most orbital called? responsible for?
- The outermost orbital is generally responsible for bonding. This orbital is often called Valence Shell
- Each element has a natural tendency to either gain or lose electrons
how are ions formed? what causes their charge?
- Sometimes during chemical reactions, atoms will lose or gain an electron to form an ion (cation, anion)
- The number of protons and neutrons do not change
- The imbalance between protons and electrons causes ions to be charged
ions and compounds
- Ions behave much differently than neutral atoms
* Neutral materials must have equal amounts of charge from cations and anions
