Chapter 1: Chemical Foundations Flashcards
Describe and discuss the scientific method
- Making observations.
- Formulating hypotheses. A hypothesis is a possible explanation for an observation.
- Performing experiments.
What is a theory?
- often called a model
- a set of tested hypotheses that gives an overall explanation of some natural phenomenon.
**an interpretation— a possible explanation of why nature behaves in a particular way.**
What is natural law?
- scientists observe nature, they often see that the same observation applies to many different systems.
- Such generally observed behavior is formulated into a statement called a natural law.
What is an observation? How is this different from a theory?
- An observation is something that is witnessed and can be recorded.
- A theory is an interpretation— a possible explanation of why nature behaves in a particular way. Theories inevitably change as more information becomes available.
Note the difference between natural law and a theory.
- A natural law is a summary of observed (measurable) behavior, whereas a theory is an explanation of behavior.
- A law summarizes what happens; a theory (model) is an attempt to explain why it happens.
What is the law of conservation of mass?
- Mass is neither created nor destroyed in a chemical reaction.
- total mass of materials is not affected by a chemical change in those materials
**created by Antoine Lavoisier
What is the law of definite proportion?
- A given compound always contains exactly the same proportion of elements by mass.
- Originally called “Proust’s law”
- Principle of the constant composition of compounds
What is the law of multiple proportions?
When two elements form a series of compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers.
Since atoms are indivisible, they will always combine in simple whole number ratios. Therefore, it would not make sense to write a formula such as Na0.5Cl0.5 because you can’t have half of an atom!
**Significance to Dalton? It made him realize that compounds are made up of atoms and that a given pair of atoms can form a variety of compounds.
What’re the 4 postulates in Dalton’s Atomic Theory?
- Element is made up of atoms.
- All atoms of a given element are identical in mass and properties. Atoms of different elements are different in some fundamental way or ways.
- Two or more atoms can combine to form compounds. A given compound always has the same elements in the same proportions. (law of constant composition)
- Chemical reactions involve reorganization of the atoms—changes in the way they are bound together. The atoms themselves are not changed in a chemical reaction. (Law of conservation of mass)
What is Avogadro’s hypothesis?
that at the same temperature and pressure, equal volumes of different gases contain the same number of particles.
What are Thomson’s charge‐to‐mass measurements?
- since electrons could be produced from electrodes made of various types of metals, all atoms must contain electrons. Since atoms were known to be electrically neutral, Thomson further assumed that atoms also must contain some positive charge.
- Thomson postulated that an atom consisted of a diffuse cloud of positive charge with the negative electrons embedded randomly in it. This model, shown in Fig. 1-13, is often called the plum pudding model because the electrons are like raisins dispersed in a pudding
where e represents the charge on the electron in coulombs (C) and m represents the electron mass in grams.
What did Millikan’s oil drop experiments discover?
Sketch the experiment
- These experiments allowed him to determine the magnitude of the electron charge value
- Using the charge-to-mass ratio determined by Thomson, Millikan was able to calculate the mass of the electron as
- 9.11 x 10-31 kilogram.
What is radioactivity?
- a spontaneous emission of radiation by the uranium, which
- three types of radioactive emission:
- gamma (g) rays: g ray is high-energy “light”
- beta (ß) particles: b particle is a high-speed electron
- alpha (a) particles: a particle has a 2+ charge, that is, a charge twice that of the electron and with the opposite sign. The mass of an a particle is 7300 times that of the electron.
What is Rutherford’s gold foil experiment?
- if Thomson’s model were accurate, the massive a particles should crash through the thin foil like cannonballs through gauze, as shown in Fig. 1-17(a). He expected the a particles to travel through the foil with, at the most, very minor deflections in their paths.
- Results of the experiment: most of the a particles passed straight through, many of the particles were deflected at large angles, as shown in Fig. 1-17(b), and some were reflected, never hitting the detector.
- Conclusions
- the plum pudding model for the atom could not be correct.
- Atoms were mostly empty space
- The center of the atom = nucleus
- NUCLEAR ATOM MODEL
What is a nuclear atom?
- an atom with a dense center of positive charge (the nucleus) with electrons moving around the nucleus at a distance that is large relative to the nuclear radius.
- The nucleus is made of protons and nuetrons and electrons orbit the nucleus.
- average diameter of an atom is 2 x 10-10 m.
- Atoms are electrically neutral. That is, they have no net charge because they have equal numbers of protons ( + 1 charge) and electrons (-1 charge).
What is an electron?
- Negatively charged particle
- The chemistry of an atom arises from its electrons.
Mass: 9.109 x 10-31 kg
Charge: -1
What is an isotope?
- atoms with the same number of protons but different numbers of neutrons.
- Chemistry of an atom is due to its electrons, isotopes show almost identical chemical properties. In nature most elements contain mixtures of isotopes.
What is the atomic number?
- Witten as subscript, Z
- number of protons
