Ch. 4

You are standing on the top of a boron‑11 nucleus. Describe the numbers and kinds of subatomic particles you see looking down into the nucleus, and those you see looking out from the nucleus.

5 protons and 6 neutrons in the nucleus; 5 electrons outside the nucleus

Why is an atom electrically neutral?

Atoms are electrically neutral for they have various subatomic particles in a single atom

Why does it make sense that if an atom loses electrons, it is left with a positive charge?

Atoms are left with a positive charge if the atom loses electrons because of the lost valence electrons.

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

Atoms are separated from each other, joined, or rearranged.

How did the results of Rutherford's gold-foil experiment differ from his expectations?

He did not expect alpha particles to be deflected at a large angle.

What makes isotopes of the same element chemically alike?

Isotopes of the same element have identical numbers of protons and electrons

What is the charge, positive or negative, of the nucleus of every atom?

The nucleus of every atom is positive

What is an atom?

The smallest particle of an element that retains its identity in a chemical reaction.

What is the atomic mass of an element?

a weighted average mass of the atoms in a naturally occurring sample of the element

How many protons are in the nuclei of the following atoms? a. Phosphorous (P) b. molybdenum (Mo) c. aluminum (Al) d. cadmium (Cd) e. chromium (Cr) f. lead (Pb)

a. 15 b. 42 c. 13 d. 48 e. 24 f. 82

What experimental evidence did Thomson have for each statement? a. Electrons have a negative charge. b. Atoms of all elements contain electrons.

a. Thomson used a cathode ray. b.

What characteristics of cathode rays led Thomson to conclude that the rays consisted of negatively charged particles?

a. deflected by electrically charge metal plates b. positive = attracts ray, negative = repels ray

What were the limitations of Democritus's ideas about atoms?

a. did not explain chemical behavior, b. lacked experimental support, c. not based on scientific method

Name two ways that isotopes of an element differ.

a. number of neutrons, b. mass number

Millikan measured the quantity of charge carried by an electron. How did he then calculate the mass of an electron?

an electron's mass is 1/1840 the mass of a hydrogen atom

How can there be more than 1000 different atoms when there are only about 100 different elements?

because of the existence of isotopes

Lithium has two isotopes, lithium-6 (atomic mass = 6.015, relative abundance = 7.5%) and lithium-7 (atomic mss = 7.016, relative abundance = 92.5%) Calculate the atomic mass of lithium.

for 6Li: 6.015 amu 0.075 = 0.45 amu for 7Li: 7.016 amu 0.925 = 6.49 amu atomic mass = 0.45 amu + 6.49 amu = 6.94 amu

How is the atomic mass of an element calculated from isotope data?

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

In the Rutherford atomic model, which subatomic particles are located in the nucleus?

proton

If you know the atomic number and mass number of an atom of an element, how can you determine the number of protons, neutrons, and electrons in that atom?

protons: atomic number neutrons = mass number - atomic number electrons: atomic number

Would you expect two electrons to attract or repel each other?

repel

How do the charge and mass of a neutron compare to the charge and mass of a proton?

the charge and mass of a neutron has a neutral charge, while the proton has a positive charge.

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

the electrons in Thomson's model were evenly spread out.

What is the difference between the mass number and the atomic number of an atom?

the mass number is the total number of protons and neutrons in an atom, and atomic numbers only focus on the protons.

What data must you know about the isotopes of an element to calculate the atomic mass of the element?

the mass of each isotope, and the natural abundance of each isotope

What does the atomic number of each atom represent?

the number of protons

Compare the size and density of an atom with its nucleus.

the size and density of an atom is larger than its nucleus

Characterize the size of an atom

very small