Chapter 4 Chemistry Questions

Why is an atom electrically neutral

An atom is electrically neutral because it has equal numbers of positively charged protons and negatively charged electrons

What is an atom

an atom is the smallest particle of an element that retains its identity in a chemical reaction

What equation tells you how to calculate the number of neutrons in an atom?

mass number-atomic number= number of neutrons

How is atomic mass calculated

the calculate the atomic mass of an element, multiply the mass of each isotope by its natural abundance, expressed as a decimal and then add the products

How did Rutherford's model of the atom differ from Thomson's

According to the Rutherford Model, the nucleus is tiny and densely packed, compared with the atom as a whole. If an atom were the size of a football stadium, the nucleus would be about the size of a marble. According to Thomson, he performed an experiment that involved passing electric current through gases at low temperature. He concluded that electrons are a component of the atoms of all elements.

How do the isotopes of a given element differ from one another

Because isotopes of an element have different number of neutrons they also have different mass numbers

What were the limitations of Democritus's ideas about atoms

Democritus's ideas agreed with later scientific theory, they did not explain chemical behavior. They lacked experimental support because Democritus's work was not based on scientific method

Use Dalton's atomic theory to describe how atoms interact during a chemical reaction

During a chemical reaction, atoms are separated from each other, joined, rearranged in a different combination. Atoms of one element however are never changed into atoms of another element

What distinguishes the atoms of one element from the atoms of another

Elements are different because they contain different numbers of protons

What experimental evidence led Rutherford to conclude that an atom is mostly empty space?

He concluded that all the positive charge and almost all the mass are concentrated in a small region that has enough positive charge to account for the great deflection of some of the alpha particles. He called this region the nucleus. The nucleus is the tiny central core of an atom and is composed of protons and neutrons. In the nuclear atom, the protons and neutrons are located in the positively charged nucleus. The electrons are distributed around the nucleus and occupy almost all the volume of the atom.

Describe the location of the electrons in Thomson's "plum-pudding" model of the atom

In Thomson's "plum pudding model" of the atom, electrons were stuck into a lump of positive charge similar to raisins stuck in dough.

Name two different ways that isotopes of an element differ

Isotopes of an element differ in mass numbers, atomic masses, number of neutrons, and relative abundance

What are the charges and the relative masses of the three main subatomic particles

Protons(+)=1 Neutrons( neutral)=0 Electrons= (negative)=-1

Compare and Contrast: Rutherford's expected outcome of the gold-foil experiment with the actual outcome?

Rutherford thought that the alpha particles would have passed easily through the gold, with only slight deflection due to the positive charge thought to be spread out in the gold atoms. What actually happened was that most alpha particles bounced off the gold foil at very large angles

What are the three subatomic particles

electrons, protons and neutrons

How did Democritus characterize atoms?

reasoned that atoms were indivisible and indestructible

How does Rutherford's model describe the structure of the atoms?

In the nuclear atom, protons and neutrons are located in the positively charged nucleus. The electrons are distributed around the nucleus and occupy almost all the volume of the atom.

Describe Thomson's and Milikan's contributions to atomic theory

J.J Thomson discovered the electron. He performed experiments that involve passing electric currents through gases at low pressure. He sealed the gasses in a glass tube fitted at both ends with metal disks called electrodes. In one electrode, the anode, became positively charged. The result was a glowing beam, or cathode ray, that traveled from the cathode to the anode. Thomson found that a cathode ray is deflected by an electrically charged metal plates. Thomas knew that the opposite charge attract and like charges repel. Millikan carried out an experiment to measure the ratio of an electron's charge to mass ration of electrons did not depend on the kind of gas.

What does the atomic number of each atom represent

The atomic number of each atom represent the number of protons in the nucleus