chapter 2

Question 1

3 points of rutherfords atomic theory

Answer 1

• 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

Question 2

problems with rutherfords model

Answer 2

atoms weigh more than they should with only protons

Their mass is due to neutrons, particles similar to protons but no electrical charge

Question 3

modern atomic theory on electrons and the nucleus

Answer 3

• 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

Question 4

what is each element determined by? what yields the mass number?

Answer 4

• • 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

Question 5

what is an isotope?

Answer 5

atoms that have the same number of protons but different number of neutrons and different mass numbers.

Question 6

what is atomic mass? used for?

Answer 6

average weighted mass

• We can use the atomic number to identify what element it is

Question 7

how do we determine atomic mass?

Answer 7

• (this is percent composition) Average Atomic mass= sum of (Isotopic mass) X (Fractional abundance)

Question 8

how is the atomic number (Z) affected by isotopes? mass number (A)?

Answer 8

• Atomic number (Z) for isotopes remains constant, while mass number (A) can vary
  
  • Only Z and chemical symbol can identify an element

Question 9

what is A made of? Z?

Answer 9

• A=#p+ + #n0

* Z=#p+

Question 10

what is the standard reference for atomic mass units?

Answer 10

• 12C - standard reference for atomic mass units (absolute value bc. Infinite zeros)
  
  • All other atomic masses are quoted/measured relative to this standard mass

Question 11

why is the mole used? what is avogadros number?

Answer 11

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)

Question 12

how was avogadros number decided on?

Answer 12

• 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

Question 13

how does a mole relate to atoms?

Answer 13

• 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?

Question 14

how is the periodic table arranged?

Answer 14

• 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

Question 15

what does periodic law state?

Answer 15

• The periodic law states that the chemical properties of the elements are dependent on their atomic numbers

Question 16

why do electrons intermingle with atoms?

Answer 16

• Because the space where electrons occupies a large percentage of an atoms volume, it is electrons which “intermingle” with other atoms. Producing chemical reactions

Question 17

what gives an atom its chemical properties?

where are electrons found?

Answer 17

• The number and arrangement of the electrons give an atom its chemical properties. • Electrons are generally found in discrete energy shelves, called orbitals

Question 18

what is the outer most orbital called? responsible for?

Answer 18

• 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

Question 19

how are ions formed? what causes their charge?

Answer 19

• 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

Question 20

ions and compounds

Answer 20

• Ions behave much differently than neutral atoms

* Neutral materials must have equal amounts of charge from cations and anions