Chemistry Chapter 0

Explain Dalton's atomic theory

1. Everything is made up of tiny particles called atoms 2. In any pure element, all atoms in that element are identical in mass and other properties; not true, isotopes of an element differ slightly in mass 3. Atoms of different pure elements differ in mass and other properties 4. Atoms are indestructible; not true, atoms are made up of subatomic particles such as protons, neutrons, and electrons 5. Atoms in a given compound are always present in the same fixed ratio, regardless of mass

Suggest two other important concepts of chemistry. Are these ideas appropriate for an introductory chemistry course?

1. We can tell a lot about what happens on an atomic scale with careful observations on the laboratory or macroscopic scale 2. The knowledge of energy changes and the probability of different arrangements of atoms help scientists predict how atoms interact.

What is a chemical change

A chemical change forms a new substance

What defines a compound?

A compound can be defined as two or more atoms of different elements that can be broken down into elements by chemical changes and combine in definite proportions

What is a physical change?

A physical change is changing state

What is a supernova? Why are they so important?

A supernova is when a star is disintegrating and spewing matter everywhere and this is important because it allows for elements heavier than iron to form

What defines an element

An element is any substance that cannot be decomposed into simpler materials by chemical reactions

What is atomic theory

Atomic theory states that atoms make up everything and each atom is composed on protons, neutrons, and electrons

How to calculate the average atomic mass of a particular element

Find the mass contribution from each isotope by multiplying each mass (in amu units) by its percent (decimal form). Then add each of these mass contributions to determine average atomic mass

What are isotopes?

Isotopes are atoms of the same element with different masses. They have the same number of protons and electrons but different number of neutrons

What is matter?

Matter is anything that has mass and takes up space, or in other words has volume

What caused new elements to form?

Nuclear fusion and stars caused new elements to form. The core of the star cooled and the area around it was so hot that it caused the star to collapse inward, forming all the elements up to iron

Knowing what we know today, which of the postulates of the atomic theory are wrong?

One postulate that is wrong is that atoms are indestructible. This is false because of the discovery of subatomic particles, such as protons, neutrons, and electrons. Another postulate that is wrong is that all atoms of the same element are identical in mass and other properties. This is false because isotopes of the same element have slightly different masses

What are Sig figs?

Sig figs are the number of certain digits plus the first uncertain digit. Digits from 1st non-zero number of the left to 1st estimated digit on the right are significant.

What happened as a result of the explosion of energy 14 billion years ago. What is that event?

The event was the Big Bang theory. It caused an explosion and then a cooling. After some cooling, nucleosynthesis occurred where only small nuclei were formed, hydrogen, lithium, and helium, due to the high temperature and pressure

What are the laws of Chemical combinations? Explain

There is the Law of Definite Proportions that states that in any given compound the ratio of elements is fixed. There is also the Law of Conservation of Mass which states that mass is neither created or destroyed in chemical combinations, it is simply conserved

Explain the various experiments that discovered subatomic particles

Thomson- his cathode ray experiments showed that atoms are made up of subatomic particles. The negatively charged particles moved from the cathode(the negatively charged electrode) to the anode (the positively charged electrode). He also modified his cathode ray tube and made quantitative measurements on cathode rays. He determined the charge to mass ratio of the particles to be -1.76x10^8 coulombs/g and called the negatively charged particles electrons Millikan- he built off the foundation left by Thomson and determined the charge of the electron with the oil drop experiment where he measured the rate of fall of drop with and without electrical charge and found it to be -1.60x10^-19 C. He then combined this with Thomson's charge to mass ratio and found the mass of the electron to be 9.09x10^-28 g. Rutherford- discovered the proton, he found out that electron removal from hydrogen gas yielded positively charged particles. He then measured the e/m of positive ions for various gases. He then performed the gold foil experiment where he shot alpha rays at gold foil and most of them passed right through. However, some of the rays bounced back at various angles showing how the mass of the atom was concentrated in the center. He called this the nucleus. He then estimated the number of postive charges on the nucleus based on experimental data. The nuclear mass baced on this number of protons was always far short of the actual mass, about half to be percise. Therefore there must be a another type of particle that has about the same mass as the proton and is electronically neutral. Neutrons were confirmed in 1932 by Chadwick.