STAAR REVIEW

How many protons are present in Hafnium (Hf) with a mass number of 178?

• 72 protons, 178 neutrons, 106 electrons

• 72 protons, 106 neutrons, 72 electrons

• 178 protons, 250 neutrons, 72 electrons

• 106 protons, 72 neutrons, 196 electrons

An atom of an element has 36 protons, 36 electrons, and a mass number of 84? How many neutrons?

• 36

• 72

• 48

• 8

What types of particles are found in the cloud surrounding the atom's nucleus?

• positively and negatively charged particles

• negatively charged particles only

• neutral and positively charged particles

• positively charged particles only

What is the mass number of a potassium (K) atom that has 20 neutrons?

• 18

• 19

• 20

• 39

Which of the following is the best description of an electron?

• No charge and the same mass as a proton

• negative charge and much less mass than a proton

• positive charge and much more mass than a neutron

• negative charge and the same mass of a neutron

An atom has 25 protons, 30 neutrons, and 25 electrons. What is the charge of the nucleus?

• +55

• -25

• +25

• -30

Tin (Sn) is a soft, white metal. Which statement accurately describes an atom of tin?

• tin atoms have five valence electrons

• tin atoms have 68 electrons

• tin atoms have 50 protons

• tin atoms have 119 neutrons

Atoms of a certain element have 11 protons and 1 valence electron. Which statement is correct?

• the element is sodium and it is not reactive

• the element is fluorine and it is highly reactive

• the element is fluorine and it is not reactive

• the element is sodium and it is highly reactive

What characteristic of an atom always determines it's identity?

• number of neutrons

• number of protons

• number of valence electrons

• location of valence electrons

Which characteristic of calcium is most closely related to its chemical reactivity?

• 20 protons in each calcium atom

• calcium's density is 1.54 g.cm³

• 2 valence electrons in each atom of calcium

• one calcium atom has an atomic mass of 40.078 amu