Which one of the following properties decreases across the periodic table from left to right and increases from top to bottom?
- A.Ionization energy
- B.Electron affinity
- C.Electronegativity
- D.Atomic radius
Correct answer
Explanation
The correct answer is D, Atomic radius. Atoms get smaller along a period and larger down a group.
Moving from left to right in a period, electrons are added to the same shell while the nuclear charge rises by one at each step. The stronger pull of the nucleus draws the electron cloud inward, so the radius shrinks; in the third period, sodium is much larger than chlorine. Moving down a group, each element adds a new shell of electrons, and the inner shells shield the outer electrons, so the radius grows; caesium is far larger than lithium. This one trend explains most of the others.
A is wrong: ionisation energy rises across a period and falls down a group, the opposite trend.
B is wrong: electron affinity generally increases across a period and decreases down a group.
C is wrong: electronegativity also increases across a period and decreases down a group; fluorine has the highest value.
Exam tip: atomic size and metallic character go one way (down and left); ionisation energy, electron affinity and electronegativity go the other (up and right).
Practice Questions
View allA snowboard pulled up by a tow rope travels at the rate of 5 m/s up a mountain. If 3000 watt of power is used, what force was applied to it ?
- A.50 N
- B.100 N
- C.600 N
- D.15000 N
Show answer
Power equals force times velocity, so the force is 3,000 W divided by 5 m/s, which is 600 N. Power is the rate of doing work: P = W/t. Work is force times distance, W = F × d, so P = F × d/t, and since d/t is the…
Read the full explanation →When a longitudinal wave moves through a certain medium, the quantity which is transmitted through the medium is
- A.material of the medium only
- B.energy only
- C.both material of the medium and energy
- D.none of the above
Show answer
A wave carries energy from one place to another, while the particles of the medium only vibrate about their fixed positions.
Read the full explanation →Which one of the following conservation laws is a consequence of the Newton's third law of motion?
- A.Conservation of energy
- B.Conservation of momentum
- C.Conservation of charge
- D.Conservation of mass
Show answer
Equal and opposite forces acting for the same time give equal and opposite changes in momentum, so the total stays the same.
Read the full explanation →A sound wave of frequency of 2 kHz has a wavelength of 35 cm in a given medium. How long will it take to travel a distance of 2.1 km through the medium?
- A.30 s
- B.2.1 s
- C.3.0 s
- D.4.1 s
Show answer
The speed of the wave is frequency times wavelength, 700 m/s, and 2,100 m at 700 m/s takes 3 seconds.
Read the full explanation →Which one of the following structure is NOT found in prokaryotes ?
- A.Nuclear envelope
- B.Cell membrane
- C.Ribosome
- D.Cell wall
Show answer
Prokaryotes have no true nucleus, so there is no membrane around their genetic material. Prokaryotes are the simplest cells: bacteria and cyanobacteria (blue-green algae).
Read the full explanation →