Chemistry Ch.2

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created 12 days ago by KC1999
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Atoms & elements
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What is an atom?

  • The smallest identifiable unit of an element

How many naturally-occurring elements are there?

  • 91

How many synthetic elements have scientists created?

  • >20

What is the atomic theory in a nutshell?

  • The concept that all matter is composed of atoms

What are the 3 most important laws that led to the development & acceptance of the atomic theory?

  • The law of conservation of mass
  • The law of definite proportions
  • The law of multiple proportions

In 1789, Antoine Lavoisier formulated the law of conservation of mass. What does this state?

  • "In a chemical reaction, matter is neither created nor destroyed"
  • Basically.. the total mass of substances involved in the reaction does NOT change *much, I guess*

In 1797, French chemist Joseph Proust summarized his observations in the law of definite proportions. What does this state?

  • "All samples of a given compound, regardless of their source or how they were prepared, have the same proportions of their constituent elements"

In 1804, John Dalton published his law of multiple proportions. What does this state?

  • "When 2 elements (call them A & B) form 2 different com- pounds, the masses of element B that combine with 1 g of element A can be expressed as a ratio of small whole numbers"

What is reductionism?

  • The idea that complex systems can be understood by understanding their parts.. including humans

When the concept of reductionism is applied to humans, what controversial questions are raised?

  • If atoms compose our brains, do those atoms determine our thoughts and emotions?
  • Are our feelings caused by atoms acting according to the laws of chemistry & physics?
  • Are our emotions nothing more than a series of atomic interactions with one another?

What is a cathode ray tube?

  • A partially evacuated glass tube constructed by English physicist J. J. Thomson in the late 1800's

What are cathode rays exactly?

  • Just a beam of e- emitted from the cathode of a high-vacuum tube

What did english physicist J. J. Thomson observe when working with his cathode ray tube?

  • That cathode rays traveled from (-) charged electrode (cathode) → (+) charged one (anode)

What did english physicist J. J. Thomson conclude about the particles that compose the cathode ray?

  • They travel in straight lines
  • They are independent of composition of material from which they originate (cathode)
  • They carry a (-) electrical charge.

What is electrostatic force?

  • An attractive & repulsive force between particles due to their electric charges

What is an electric field?

  • The area around a charged particle where electrostatic force exists

What is the charge of a single e-?

  • - 1.60 x 10-19 C

What's the mass of a proton in amu?

  • 1.007277 amu

What's the mass of a neutron in amu?

  • 1.008665 amu

Whats the mass of an e- in amu?

  • 0.00055 amu

What are the 3 types of radioactivity?

  • Alpha (α) particles (+ charged, most massive)
  • Beta (β) particles
  • Neutrons
  • Gamma (γ) rays

Whats the 1st basic part of the nuclear theory?

  • Most of an atom’s mass + ALL of its (+) charge is contained in the nucleus

What's the 2nd basic part of the nuclear theory?

  • Most of the volume in an atom is empty space, within that space is where e- exist dispersed

What's the 3rd basic part of the nuclear theory?

  • There are as many e- outside the nucleus as there are protons within the nucleus → making atoms electrically neutral.

If matter really is mostly empty space, according to Rutherford, then why in the hell can you slap your hand on a table & feel a solid thump?

  • Matter only appears solid due variation in its density → its on such a small scale that our eyes cannot see it → thus brains don't process it
  • I don't like that.. mm

All atoms are composed of the same subatomic particles, just in different proportions. What are those particles?

  • Protons
  • Neutrons
  • Electrons

In SI units, whats the mass of a single proton?

  • 1.67262 x 10-27 kg

In SI units, whats the mass of a single neutron?

  • 1.67493 x 10-27 kg

In SI units, whats the mass of a single e-?

  • 0.00091 x 10-27 kg

What is the assigned charge of a proton?

  • +1

What is the assigned charge of an e-?

  • -1

Which subatomic particles must be equal in magnitude to each other in order for the atom to be neutral or sum to a zero charge?

  • The protons & electrons
  • They are the only particles with charge

Why is matter normally charge-neutral?

  • B/c protons & e- are normally present in equal numbers

What's an example of matter dealing with a charge-imbalance?

  • Lightning! → build-up of (+) charge on ground & (-) charge in clouds → electrical discharge (lightning) occurs → equalizing/ correcting charge imbalance

What's the most important number to the identity of an atom?

  • The # of protons in its nucleus
  • This literally defines the element

What is the # of protons in an atom's nucleus called?

  • The atomic number
  • Represented as Z

Each element is identified by its own unique atomic number but also with a chemical symbol directly below it. How is it formatted?

  • As a 1 or 2-letter abbreviation

If the atomic number of an element is 2, the chemical symbol must be He. Why?

  • B/c He has 2 protons

All atoms of a given element have the same # of protons. However, they may not have the same # of what?

  • Neutrons
  • Ex: ALL Ne atoms contain 10 protons, but they may contain 10, 11, or 12 neutrons → each varying slightly in mass.. makes sense

What are atoms with the same # of protons, but different #'s of neutrons called?

  • Isotopes

What does the # of protons + the # of neutrons of an atom equal?

  • The mass number

How are isotopes symbolized?

card image

When do neutral atoms become ions?

  • When they gain or lose e-