Aliens sure have got it in for us in the YA-lit adaptation “The 5th Wave.” Shortly after their gargantuan ship appears in the sky, all “Independence Day” portentousness, they cut the world’s power with an electromagnetic pulse in their invasion’s first wave. Then it’s city-leveling quakes and tsunamis. Then a deadly pandemic. Then a body-snatching infiltration campaign. So we know that fresh hell number five is going to be bad, all right. Turns out it’s bad scripting.Chloë Grace Moretz performs quite capably as Cassie, our rattled, resilient teen heroine, until she finds emotional connection amid the chaos, and the story’s dialogue and tone turn laughable. Moretz’s material isn’t necessarily the dopey stuff, but there’s plenty to which she’s forced to react, and it’s consistently distracting. Equally self-defeating: It keeps the movie from more fully articulating intriguing themes about humans being robbed of their humanity. It’s tough to stay focused on the provocative bits when soapy talk of teenage yearning and angst keep making us snicker.The action opens midstream with Cassie already very much in survival mode, packing an assault rifle and facing down a dicey situation in a ransacked convenience store. Director J Blakeson then just as effectively cuts back to Cassie’s life before Armageddon, when she was just a typical Midwestern girl with typical preoccupations: hanging with girlfriends, checking in by curfew with her dad (Ron Livingston), nursing a crush on hottie classmate Ben (Nick Robinson, “Jurassic World”). So carefree, so alien-free.Cassie lands in a refugee camp, where things don’t go well for her father, and she winds up separated from her traumatized little brother (Zackary Arthur) in a military evacuation. There’s some solid writing in Cassie’s somber inner musings about the questionable ways that circumstance is changing her. (You’ll forgive these voiceovers if they seem a tad eloquent for adolescent diary scribbling.) But oof, the exchanges she shares with Evan (Alex Roe), a hunky, enigmatic survivor who agrees to help her find her brother. And there’s not quite “Hunger Games” credibility to the evacuated kids’ reconditioning as junior warriors, led by Liev Schreiber’s serviceably flinty colonel but also by Maria Bello’s bewilderingly Kabukified propaganda officer.Meanwhile, that ominous final phase of the title is delayed and delayed for an eventual Big Reveal — but it’s less a twist than a culmination of all the ham-handedness. You’ll be more than ready to wave goodbye.THE 5TH WAVEDirected by J Blakeson. Written by Susannah Grant, Akiva Goldsman, and Jeff Pinkner, based on the novel by Rick Yancey. Starring Chloë Grace Moretz, Nick Robinson, Alex Roe, Liev Schreiber. Boston Common, Fenway, suburbs. 107 minutes. PG-13 (violence and destruction, some sci-fi thematic elements, language, brief teen partying).